Why do we need ModLoader or modified vanilla vpp_pc files, again? I extracted the tpf file with TPFextract, renamed the dds files to tga.dds (to match the original names), and used them to replace the textures from sr3_city_awld.gpeg_pc (sr3_city_0.vpp_pc -> sr3_city_awld.str2_pc -> sr3_city_awld.gpeg_pc). Then I just repacked sr3_city_awld.str2_pc and updated the asm (stream_grid.asm_pc), and placed them both into the game's root folder. The new textures are in the game.
With fewer details: extract the texture files, replace the original textures, pack everything back into the STR2 (no need to repack the VPP), update the ASM, and place the updated STR2 and ASM files into the game's folder.