I have updated the x86_64 Engines Pack with a fixed MAME compile which was missing the no-nag code. Sorry for any frustrations caused. Hopefully, with the correct rom version, PicoChess should no longer freeze when using a rom with known issues (and no pop-up warning window should appear with retro artwork enabled). Perhaps Johan can update his x86_64_mame_lite.tar.gz resource file.
This also works in PicoChess v3.4 but requires more effort to install on x86_64.
The link to the Engines Pack is the same:
If you just want the corrected MAME file (mess), you can download it here:
Randy