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.
IPL search order iplrom, iplromxv, iplromco, iplrom30 and font cgrom30, cgrom30.tmp, cgrom, cgrom.tmp (SDL/SDL2/winx68k.cpp:277-331), SCSI ROMs (:140-271), all from $HOME/.keropi (SDL/prop.c:172-194). One IPL and one font are required: without them the CPU loop never starts.
Abdessamad Derraz