By either replacing the textures directly or just rewriting the texturepaths
*edit*
Sorry i just read the whole thing now
Well first of:
A m2 is a single,smaller model. Like characters. They can be animated an stuff
A wmo is a house or more complex stuff.
They both use the .blp file format as textures. This is the official texture format that blizzard uses in nearly all their games.
What you want to do is the stuff phucko1 said.
First off download some programs ,most of them can be found in the tools section.
You will need a mpq editor to open mpq files(a mpq is a thing sort of like a .zip or .rar file, it conatins many other files with a folder structure) and wowmodelviewer to find the models you want to reskin.
In modelviewer you can for example extract those texture that are used in the model.
If you enable in the export function the "preserve path" checkbox ,those files will get extractet into the same folder structure as they lay in the mpq files.
Go then into the export folder of wowmodelviewer and use a converter on the .blp files.
Also this can be found in the tool section
Then use a program that you like to change the textures , save them and convert them back.
Then follow the instruction of this guide to build your patch file:
viewtopic.php?t=41There is some stuff that you will have to learn first.
Look into this guide:
viewtopic.php?t=98to find out more about the file formats and sturctures used in wow.
If you have any further questions don't hestiate to ask
(But not via PM! Use the forums to let yourself help and help with that other users too!