The same way you'd convert an outfit to another Bodyshape -- create a project based on the texture you want (I call it Donor, so I know what to delete when I'm done) and other based on the mesh you want (I try to give it a meaningful name, like AF-Blockfoot). Export from both projects, copy the bitmaps from Donor to AF-Blockfoot (allow to overwrite), load and save AF-Blockfoot. Delete Donor and make a new Donor from the next texture, and repeat.
Here's a more patient explanation of how to do this:
http://www.sunsims.com/forums/showthread.php?t=774
Unfortunately, Gothplague's cool tute with pictures went the way of all electronic flesh in the InSim debacle...