RetroPie builds minivmac/minivmac, winterheart/quasi88 and TurtleBazooka/px68k under the package names minivmac, quasi88 and px68k (scriptmodules/emulators/minivmac.sh:12, quasi88.sh:12, px68k.sh:12). With built_by retropie and those names in cores, RetroPie resolves them to minivmac37, quasi88kai and px68k-sdl, while its libretro builds stay reached through retroarch. Measured: RetroPie keeps 532 of 532 platform files OK and gains the 14 files the standalone builds read; no other platform's resolution changes.
The SDL build reads vMac.ROM, fixed at build time to the Mac Plus ROM name and 128 KB (setup/SPCNFGAP.i:60-63), and checks it against three Mac Plus checksums (src/CONTROLM.h:1344-1388). Search order: --rom, the executable's directory, mnvm_rom/ under the SDL pref path, the working directory (src/OSGLUSDL.c:546-620).
Abdessamad Derraz