Every now and again cores are updated and new features added or bugs are fixed. In most circumstances this is a good thing but just occasionally and especially with MAME or libretro-mame it can be a nightmare for your ROMS!
Updated libretro-mame cores usually mean an update to which version of the MAME romset it supports, nearly always the latest MAME release.
So, lets say that you have installed Retroarch and the current libretro-mame is version 0.214 (It tells you the MAME version in the left hand corner of the screen when you load the core) and you have downloaded and filtered your 0.214 romset. The last thing you need now is to update the core and find that it now only supports a newer version of MAME.
The easy way to remedy this is just to rename the MAME core to something else, this way it can’t get updated and will support whatever version of MAME it does right now.
just rename the following files:
/cores/mame_libretro.dll >> /cores/mame_214_libretro.dll
/config/mame_libretro.cfg >> /config/mame_214_libretro.cfg
/info/mame_libretro.info >> /info/mame_214_libretro.info
Finally, edit the newly renamed mame_214_libretro.info file and change
display_name = “Arcade (MAME)” >> display_name = “Arcade (MAME 0.214)”
Reload RetroArch and the core will be named MAME 0.214, you can of course now re download a new MAME core and it won;t affect your existing MAME setup.