Is it at all possible to affix negative stats to weapons and other equipment, specifically negative values for PA, MA, Speed, or Jump?
You can using an ASM hack from FDC to allow for negative Jump. (You can find his thread in the Important Links in FFT Hacking.) However, it means you cannot make use of the "Stepping Stone" property of monsters/etc and will need to fix their Jump values due to how it works, and I am not sure if it will display properly when equipping the items in-game as I have never personally used it. Otherwise it should work fine.
Thank you very much!