Mods that do not modify graphics, or hack Cave Story should probably can be ported easily.
If they modify graphics, you have to make sure they are bmp files, and at the right size graphics...
I think you can use original graphics with modifications if you create a "ogph" folder in your mod folder (and they are bmp).
HMh...
I think actually, you might have to modify stage.tbl if the stage has a different tileset choice than the original. That can be a little tricky; make backups... I used XVI32 to carefully make changes there...
I don't know if there's an easy tool to edit stage.tbl?
Some little warnings... It might be better to just make a different CS+ copy for each major mod at the present time. I believe that even if you change the portraits (Face.bmp) or images that modify chests, etc (NpcSym.bmp); it might still use either the original base folder or Xmas for portraits.
I should confirm that...
Also, there isn't a whole lot of space for adding mods in the challenge screen. It quickly goes off the edge of the screen when adding a few to the original challenges...
There really needs to be a seperate MODS section, that is scrollable...