Opcode 0, Timing mode 1 does not leave any effect behind to be removed. It directly changes the AC stat in the creature file. You'll need to use timing mode 9, or 0 with an arbitrarily large duration (126144000 = 48 in-game years, can't go much higher because its converted to ticks (x15) and still has same field size(4bytes)). Or timing mode 4096, duration = 0x7fffffff.
Most opcodes with a relevant CRE stat do this when using timing mode 1 (or 4 or 7, which convert to 1 after their delay).
Base, Specific, and [All Weapon] AC
Resistances (excluding magic damage and poison)
Saving Throws
Attributes
Base Thac0
Lore
APR
Current HP and Damage (obviously)
Max HP
Kit
Animation
EA/GENERAL/CLASS/RACE/ALIGNMENT/GENDER/SPECIFICS
Thieving skills are a mixed bag, the older opcodes do (59/90/91/92), the newer opcodes do not (275/276/277).
Comments
It directly changes the AC stat in the creature file.
You'll need to use timing mode 9, or 0 with an arbitrarily large duration (126144000 = 48 in-game years, can't go much higher because its converted to ticks (x15) and still has same field size(4bytes)).
Or timing mode 4096, duration = 0x7fffffff.
Most opcodes with a relevant CRE stat do this when using timing mode 1 (or 4 or 7, which convert to 1 after their delay).