I think that adding your ideas to the world is great! Doing so you create your own world and not using that of WOTC(umm maybe not entirely).

I like to respect the archetypes of races, while being realistic about the fact that cultures are diverse. African American culture is far different from Haitian culture, but they belong to the same race.

In the same sense, dwarves living in a resource rich mountain are probably completely dissimilar to a group of dwarves living in a hill side, living in constant vigilance of the nearby hill giants.

A culture adapts to their sorroundings, and in game this can translate into the rich mountain dwarves losing part of their bonus to AC vs. giants, but get a much bigger bonus to appraise chacks.

Meanwhile, the hill dwarves don't have much time to look at pretty gems and metals, but spend their entire life learning how to defend themselves against giants.

In my campaign world fracturn, I decided that elves adapt magically to where ever they're born. An elf born in the woods is a wood elf. And elf born in a city is a high elf, etc.

The disconnection from this ability for half-elves is a big part of their identity as a race.

In the campaign I'm in right now, there were things that stayed the same and things that were modified, so it was a mixture of both.

Classes, feats, and prestige classes directly drawn from the books are for the most parts unchanged due to balance concerns. The really major changes were: PCs can pick the Noble class (from Dragonlance, I think) rather than the Aristocrat NPC class, in addition to the Favoured Soul class and two homebrewed classes that had to do with the game's techno-magic theme; a few prestige classes were modified, such as the Arcane Archer being renamed, granting +1 to caster level every other level and losing the ability to fire magic arrows, etc...

Of course, there are homebrewed prestige classes, with some being meant mainly for NPCs. For example, there are airships, so there is a 5-level Airship Captain PrC.

Races ended up having a lot of small changes that, in the end, made them more powerful than the core races. There are also new subraces. The main effect this has had on the campaign is that picking monster races or taking templates actually ends up making you weaker than it normally does.

For example, humans have a +2 racial bonus on Diplomacy and Gather Information checks, and +2 on saves vs fear. They also have a subrace, the Highborns, who are meant to represent men and women whose blood lineage can be traced back to the greatest leaders and heroes of legends, and as a result get special abilities such as inspiring their allies in combat (+1 to hit, +1 to save vs fear) but get a +1 LA.

Overall these changes have made the campaign feel like 'high fantasy' in addition to a very distinct Warcraft-like feel.

I think there's a 5-level airship captain PrC in the Eberron Explorer's Handbook.

I'm personally not so attached to the sacred cows of D&D (elves, Vancian magic, etc.) that a little or even a lot of houseruling would scare me away. If it becomes d20 Fantasy instead of "D&D," then so be it.

What's important is that your players know what the changes are beforehand to avoid any misconceptions going into things.

There's nothing wrong with playing d20 Modern in a fantasy setting. d20 Past has lots of rules for lower tech eras.

I'm a big fan of d20 Modern. I've enjoyed every game I've played in it, regardless of setting.

I think it's the design of the base classes, and how a lot of the advanced classes really seem to have some unique and interesting traits.

I'm actually deciding if I'd want to use d20 Modern as a base instead of D&D. I want to change magic around, but I think I want it to still be present and significant part of the world. Is it easy/possibile to adapt tech as magic from d20 Modern?

I think the best way to do it is like so, and you and your players will have to remain flexable during the rewrites.

Start with the core rules as written and work your setting into that. This is a good solid base to begin even though you may feel that parts of it are not to your satisfaction.

Then, changing only one rule at a time, play though some adventurs with a ballanced party. As you agree that one rule change is acceptable then move on to the next. When doing something like this sweeping changes all at once are not going to help you much.

Prioritize by changing first the things you think are obviously broken before moving on to the stylistic changes.

And finally, there is a tone of variant rules out there, don't forget them when seeking alternatives.

How do you do that for stuff like changing character races? I mean, if I suddenly decide elves don't exist in this world, what happens to that elven PC?

It also seems like some things (like maybe reworking the magic system entirely) can't be done in steps--a system has to be set up all at once.

Though I've thought about doing stuff like that for the combat system to work it out (like I want to change HP to wound/vitality, then add special types of wounds; and take AC and maybe convert it to armor as DR, then figure out that stuff).

Thanks.

Putting your ideas into your game sounds like a good idea to me.

Sometimes there are teething problems, but once the bumps are smoothed you usually end up with memorable games for the right reasons.

Changing the campaign world is one thing, changing the game is another. IMG, the entire campaign takes place at sea and on island, there are continents on either side, but the party has no reason to go there. There's an 18th century level of technology, but I still use all the core races and classes, allow nearly any PrC, and I find myself using more core material than I have in previous campaigns. You can make a radically different game without changing the content too drastically. I achieved that with just a new setting.

Whenever I come to a game and someone claims they've changed the magic system or combat system, I am skeptical. I have no real quarrels with the current system and I feel like the ideas of the person making these rules might not gel with the rules that are getting made. But lack of faith is my own issue, and likely has more to do with my relationship to the DM of the moment. If your rules are good then good, but the skepticism is a hump I'd have to get over as a player, and the more you'd changed the bigger the hump.

Actually I'm thinking of making a kind of sea world--this is part of the inspiration to use different races and maybe classes so that the world actually feels somewhat different (like I want to use some of the races from Stormwrack, but don't want to have that many kinds of civilization, so want to get rid of some of the core races).

I generally want to keep mechanics the same (it's still d20). I just wish the combat system was a little more involved: I want being wounded to be more than just marking your HP as a lower number. I want a character to have to deal with the fact that he's just been stabbed in the arm! My group had a combat system like this in 2e, the only problem being that resolving attacks could often get slow (though we had a small group so it worked out). I want to try to add a level of complexity that makes battles more than just swing-damage-swing-damage. I'm not sure what I want to do about magic, but I feel like I have to do something because I don't like the feel of magic currently--it doesn't feel "magical" or special in any way. So I'm not sure how exactly to change that.

Though I do understand your skepticism. That's kinda what I'm trying to test the waters for--how big a hump can I make before people won't want to climb it.

As long as it's clear what the changes are ther's no problem. There are a lot of other D20 fantasy games out there that have different systems for things already, if yours works then cool.
Sounds like a good idea to put the ideas out there, there are a lot of people on here with good ideas and can probably help mold concepts to be a quality finished article; or just discuss them generally.

In my new game I've kept most of the core races there with minor changes. I eliminated Gnomes and Halflings (always tell people that I don't believe in them), but otherwise Elves and Dwarves are in there. Take a look at my site at www.westendforest.com for more information. You're welcome to adventure in my setting if you'd like.