Adding custom missions

[Kade]

is it possible to add a custom mission on ps2 disc? like in instant action? if not can i edit a default instant action mission for the ps2?

[Dark_Phantom]

You can only edit PS2 files once they are taken off the disc, then you must recompile it back into an iso file.
If you put it on a disc, it will not work unless the PS2 is softmodded (plus if you use the disc method you're going to waste a lot of discs).  Unless you have done this, it will only work on an emulator.

[Kade]

so basically im using a ps2 disc on the ps3. does this change anything?

[Dark_Phantom]

Nope.  Still needs a modded console and the rest still applies.