By "unacceptable" I mean the emulator marks them as "unacceptable" within the firmware manager, represented with a thumbs down icon. They would also not be automatically picked up in BizHawk's firmware folder, you would need to manually bind them, at which point you'll end up seeing the thumbs down icon. What you're doing is strictly a power-user type deal, like forcing wrong regions into firmware slots, with no guarantee it will work (and might or might not be grounds for rejection for TASVideos itself).
Regardless too, skipping some BIOS intro or whatever by just using a different (unsupported) BIOS file is just completely pointless for a TAS here: it just doesn't count as an improvement. We do not just use raw numbers here (there are many cases of TASes with longer movie time obsoleting movies due to having gameplay improvements, with the longer movie times ultimately coming from emulation/other non-gameplay differences), and trying to lower the time with just using a different BIOS file is more of a "cheap shot" to be frank.
