Editing .mdx files to have different skinned models

I've been downloading some skins for different units, and I want to have both the original unit with the original skin and another unit with the new skin.

I opened the mdx file(in this case Jaina.mdx) as a txt file. Then I edited the part where it says "units\Human\Jaina\Jaina.blp" to say "units\Human\nskin\nskin.blp" . I did the same thing for Jaina_portrait.mdx . I then imported the skin and those two files into my map. I changed the path to the appropriate one, but when I tried to put my new Jaina in the map it only shows as a green and black cube (in game it shows nothing except shadow). :(

Anyone know why this happens?
Is the problem that mdx files can't be edited this way?
If so, does anyone have an alternate way of achieving what I wanted to do?

Any help is greatly appreciated. :D

I believe you have to convert it to .mdl, edit, and then convert back to .mdx.

go to wc3 warehouse, then to tutorials, and there is a good mdl editing tutorial for what you need.