[scorpio_rocks]

Without entering into the argument about helicopter survivability (mine seem to fall out of the sky if looked at harshly!) to answer your questions:

No the ONLY way to change helicopter armour or ECM or AA systems' damage/hit probability/etc is to use MobHack (which is actually really easy!). [the front steel armour value is the 'durability' of the airframe, and the side hull armour value is the 'armour value']

and No it will NOT be PBEM friendly (both players must be using the same OOBs) You could send your opponent copies of the altered OOB files if they agreed to your arbitrary changes.