I'm working on a landmass mod that was pre-built. Any replacers (mainly for terrain) don't change the look of this continent. I assume maybe they're different textures than what MW uses, so the new replacers won't recognize them. I know there are a few texture replacers out there for terrain (Vibrant Morrowind, Darker Morrowind, and others). I'm curious to know what it would take to allow this continent to accept replacers so that it could be consistent with any changes made elsewhere in the world and whether I could do it myself. I've also never done anything like this before, so i'm sure there's much more to it than I might think. Any ideas?

you could rename the texture replacer's ti the same name as the ones used in this mod ie:

if the mod made has a texture called tx_BT_moss
and darker morrownd replaced the texture TX_wg_moss or something you could you could go in to the darker morrownd files
and select TX_wg_moss copy it in to a new file rename it tx_bt_moss and copy t nto your texture file

just a suggesestion as i didn't really get what you went

You would have to reassign the textures to point to ones used in vanilla Morrowind.

You would need to copy the contents of the Construction Set CD's textures folder (and/or Tribunal and Bloodmoon's textures folders) into your Morrowind Data Files folder first.

This tutorial is for Oblivion, but the procedure for Morrowind isn't much different:
http://cs.elderscrolls.com/constwiki/index.php/NifSkope_Alchemy#Base_Textures

Just as a note: Textures marked with _n are not used in Morrowind. Underscores are fine.

So I know it's been a while since i've posted here. Would I be copying the contents to see the names of the files, then switch the landmass mod to match those names? I guess i'm still a bit confused.