I don't know anyone that has this game so i cant get the rendezvous or melee exclusive weapons and i was wondering if there was a way to edit them into my inventory or the shops inventory.
The short answer is: get a PSP. You can hack PSP saves, or run Gameshark-like programs as background processes. Or go the free way and play it on PPSSPP. But no, you cannot hack Vita saves. I don't even know of a free way to hack PS3 saves, honestly.