Hi
As long as your character kinda fits to a human that would work. What not really works, is that you add stuff like tail or wings, which can be moved. There are simply the bones missing. Yes I did a test even for that. But it was a hack and it was years ago. The new version will be more flexible, and one could do that, but who will create all the targets?
http://www.makehumancommunity.org/forum/viewtopic.php?t=16927So anyway, for a proxy simply use MakeClothes, Assign your new character as clothes, the standard one as Human. Be careful with vertex groups, I would propose to do one for each leg, arm, body and head.
The .mhclo file must be renamed to .proxy and put into the correct folder.
There are limits: Makeclothes (and makehuman internally) use an approximation algorithm based on barycentric coordinates, so 3 vertices near the vertex you want to create. Classically that means that too much distance to the original character will fail, but also when you use a lot of geometry where only a few vertices are around or the other way round. Sometimes it looks fine on the standard until you move the first slider in makehuman or pose the character.
Greetings
Punkduck