there's a few different firmware version "requirements"
the most basic one is the 'required system version' as specified in the content meta. for some reason the system saves required system version to the title database (or w/e) separately and the value in the content meta is never read again after the initial install. tinfoil has the setting to choose if you want to bypass that check or not, dbi always does it because there is no downside to doing it. all it does is write the lowest possible value to required system version in the title database when installing a nsp instead of using the version specified in the content meta, the actual game files are untouched and signatures are not broken so it works without fs or loader patches
next is the master key encryption, it's trivial to decrypt a nsp and re-encrypt to a lower master key if you want. it will break signatures and require fs and loader patches to run. converting to a lower master key is not necessary if you use fusée to boot because it directly generates all the latest firmware supported master keys or something instead of getting just the ones supported by the actual firmware version. if you use hekate then you have to decrypt and encrypt to a lower master key, with fusée the game will install and run fine even if the master key is higher than your firmware, as long as...
and last is the sdk version the game was built on, you are not bypassing this unless you can decompile the game back to source and port it to a lower sdk. a game on a slightly higher sdk might work on a slightly lower firmware, or it might not. it probably depends on if the game actually uses new functions that are not supported in older sdk, or if the new sdk functions are significantly rewritten compared to the old sdk, but you should probably just update your firmware version to at least match the sdk version to avoid problems
