@claudiazan quote totally.
I tried too but to no avail.
totally missing a reference site, the code and minimal explanations not on the code but on the functions of the ready image, they do not help absolutely) the only 2 authors are those who can lead the way.
there are 2 important things. the first, as you rightly did, try to change things, through the configuration files / crt / bin..etc .. which you simply access via the network, which can be read, modified and saved on the fly. and are visible via the network (wifi) in the network folder of the pc / windows when you turn on the PI / crtevo (obviously configured with wifi) ... therefore easy management of roms, bios but also of everything (or almost) necessary to carry out various changes including the inclusion of a new system not present in the official version today.
the second important thing, is that probably there are important files to know (and modify or insert) ALSO in the "retropie" section that the network does not show you .... folders you access only with FPT softwares, and some files among these are not editable (you need a linux system and deep knowledge of permissions ... otherwise you ruin the partition making it unusable on SD)
you were talking about DOSBOX, and in fact it is enough to easily access the RETROPIE configurations from the CRTEVO menu, install the additional DOSBOX package, add games in the appropriate compatible way, in the specific ROMS directory called PC .... to see it work without any message incompatible system.
unfortunately as you have rightly noticed for other packages / emulators the same thing does not work, and it is certainly not a graphic resolution limit problem, exact vice that emulates the famous 8 bit commodore, it is not different from lr-vice (the one already present ) ... the problem is that vice is not part of retroarch, while lr-vice is. VICE is more powerful than Lr-vice both in terms of functionality and options, and as an emulation, so much so that it allows you to emulate other commodors and not only the c64 (see vic20 in fact) ...
so probably to make it work (vice) and not see that horrible incompatible system writing when you try to start a test game, it's not enough to install the package from retropie, but files / strings must be added ....
And here I am totally on the high seas like you.
it would be nice to start from here, to understand how to do it, one thing is sure, I do not think it is necessary to start from a still virgin image to be unpacked, but you can work a ready image, precisely through what you access via the network, and via fpt.
possibly if no one is interested here, please write in private, maybe in 2 by dint of attempts we can do something.