Postal can open up Sims 3 package files, let you poke at their innards, change things around, then save them back into new package files. Postal can navigate all kinds of Sims 3 package files, and parse/display/write many resources, including OBJDs, OBJKs, STBLs, XMLs, CSTRs, GEOMs, NMAPs, DDSs, PNGs, VPXYs, Texture Compositors and the various text-based formats. The Postal Editor is built on top of the “Postal API” which has already been used in other tools, including The Sims 3 Mod Generator and Merlin.
The latest version of the Postal installer can be downloaded from Sourceforge.
Postal extracts .obj files from the geom to enable users to modify the mesh.