I made a system to modify unit stats when they are loaded, instead of having to do so after the fact or by using a separate character slot. The unused byte +0x6 in UNIT data, next to unit flags in EA or labelled ?? in FEBuilder, is repurposed as an index to a stat modifier table. You can see the Pirate up above has unusual stats and nonzero Con/Move modifiers as an example.
All main stats from HP to Luck, as well as Con and Move modifiers, are available to be changed. For those using the Str/Mag split, Magic is also included as a potential option.