You need something like stuffpbo to make a folder a PBO again. I don't know if the downloads are working, but you can find it in the editors depot (
http://www.ofpec.com/editors).
Im going to assume you copied your new textures over the top of the old ones, rather than changing paths.
You will need to make your folder a different name if you dont want to overwrite the original work. An author tag usually works.Ill use mine for this example. PTY. Have everything you want in the PBO in there, eg textures, model, config
So say i took an existing guy and edited it, say if there was a pbo called soldier.pbo, with a model in it, soldier.p3d
Now i want to retexture it, so i call this guy PTY_soldier.pbo, so i dont write over the original soldier.pbo
In order to do this, the model path in the config file has to point to, for example "\PTY_soldier\soldier.p3d"
This will enable the model to get ingame. But you also need to change the texture paths, as at the moment they are still \soldier\texture.paa, and you want them PTY_soldier\texture.paa.
SO open up o2. in the final drop down menu at the top, there is "Texture library", open this up and you will see a list of textures in use. Press down shift (i think, try control if it doesnt work) and double click the texture you want to change. You should see all the vertices which contain that texture have been selected. Now right click on the modelling window (but make sure you dont move anything) to get back into it, and press "E". At the bottom, you will see a texture path. Change it to suit you. In my example, "\soldier\texture.paa" to "\PTY_soldier\texture.paa". Click Apply, be sure to check its worked in buldozer. Do this for all the new textures.
Thus when the model is loaded ingame, you should have a model appearing with textures.
All you need to do now is, load stuffpbo or a similar tool, select the addon folder (eg PTY_solider) and ask it to save as "PTY_soldier.pbo" in the OFP addons directory.
Hope this helps, if not, wait for Planck!