For these you have to take the value away from ff ff rather than add it to 00 00, so to have a weapon ignore defence you actually have to type in ff fb, to take away MP it has to be fe ff, and so on.
By the way, have you come across this tool for hexadecimal <-> decimal conversion?
http://www.statman.info/conversions/hexadecimal.htmlEDIT:
To put paralyse on a weapon you must change 0x05 to 19. But it seems that you want to guard against it, so change 0x06 of your armour. I haven't tested this, so it might not be reliable. I don't know whether you can make an armour cause peerless; they might be able to guard against status change but I doubt they can cause it. Normally one would use an accessory for something like this (at 0x05), and I'm not sure how one could start a fight with peerless.
EDIT 2:
Deathblow, if you are still wondering how the A0 attack power modifier works, I have found that it takes into account the user's status afflictions, whoever that user may be. So, it will activate whenever the person using the weapon has those status afflictions.
I have also discovered that the attack power modifiers used on weapons also work for other the attacks in kernel.bin1. So, for example, you could have the attack power of fire determined by the users MP/MaxMP.