Is there any way I can temporarily undo the changes made with the .exe optimizer patches so I can use MCP, or am I doomed to reinstall?
The exeopt documentation I have says:
The program automatically generates backup files. To restore a backup, just select the executable file as if you were going to patch it, then click yes on the dialog box that appears. (The backup files are named ***.fpu2ssebak, mainly for people who are using this after my fpu2sse frontend.) Clicking cancel in the dialog box will result in the patch being canceled, and clicking no will patch the file anyway, and not create a backup file.
So you should be able revert. If not, you might try installing Morrowind to a temporary directory and just use the Morrowind.exe from that. It's always good to have a fresh copy of Morrowind around, just in case you want to check how something was in its original state ... if you have the space.