I'd like to make changes to an existing mod. It's an entire continent, and before I accidentally deleted my modified .esp and all of it's data files, I was going to change the entire continent and save it all as one .esp. Since there are many areas that need improvement, i'd now rather take the approach of changing one area at a time and using the new .esp to overwrite the continent and apply these changes smoothly. Then repeat this for as many areas (or other improvements such as dialog among many others) as I need to. Eventually I may string all of these mods together to include them all in one convenient .esp. But as for now, i'll stick to the main question:

If I create a new .esp which makes changes to the continent, what do I have to do in order to cause the new .esp to overwrite the continent and become a part of it (such as making mods that overwrite vanilla Morrowind for example)?

Make sure that the modification plug-in (mod.esp, for example) is set to active, and the original plug-in is set to passive (if the original mod is a master file, then it will say master, not passive) while you are making changes in the Construction Set. Then just load both the original file and the mod.esp file when you want to play and the changes in mod.esp will overwrite the old stuff in the original file, since mod.esp is newer.

Hmm. That seems simple enough. Thanks for the quick reply.