Tried out the "Mega Items" option today to see what it would do or how it would work. When i read it right, then the goal was to have several weapons to "upgrade" and still having the base weapon there for other upgrades.
Yet all 99 of that weapon get upgraded at once, and there is no real way to split this stack of 99 either. On top if you put the complete stack into your storage with Jin, you are unable to get them back out again - and also unable to delete them.
Seems to work fine with the ingredient items, just not with the weapons themself. So either leave the weapons at singles.. or find a way that they are actually able to be splitted or that only 1 is used
PWizard stated at some point in this thread the reason why( im too lazy to go through and find it) and i think the reason was something about there not being a way for the trainer to tell the difference between a weapon and a item due to how the game is coded. So your best option when using the mega item cheat is to give your weapons to the mechanics daughter (something starting with J i cant remember right now) and turn it off then get weapons back and you'll have 99 of all your items and only 1 of the weapon.
[Edited by csos95, 10/13/2011 3:26:29 PM]