Okay, this is what I did before (although I experimented more with it) and I also did the same thing today as a test.
1. Copied an instrument definition file to a new one called test.ins (picked one, selected it, copied it, then pasted it to a folder... so it is a cake produced ins file, then renamed it test)
2. opened it with wordpad (it said it was too big for notepad)
3. the file was very large, so I copied the beginning part of the file (down to the first 0= ). That way it included some of the heading stuff
4. change the name in parenthesis to something like "test kit"
5. changed the name of a few patches and resaved
6. tried to import it in inst definitions and was told (rudely I thought!!!) by cake it was not an inst def file
So, because I am compulsive, I tried a few varieties, such as open a smaller inst def set and deleting only 4 of the 5 banks that were there (one bank of patch names was intact)... tried to rename 2 or 3 and resaved. When I opened it, there were no bank names saved at all.
I don't know much about this stuff, I wonder if there is some formatting convention that I am overlooking when I type in names like follow each name with five returns or something. I have tried very hard to leave the heading info and other stuff alone. When I import other files (like from lil chips) or make my own the old fashioned and slow way (like inside cake or hopefully sonar)... it works okay, but takes forever. If someone figures out how to edit these in a text editor, I'm there!!!
Good luck!