Would this work...?

Im too lazy to try it out but would it work if just before you killes somebody you recorded the packet and then played it back like 500 times would it be like getting 500 kills and youd get that much EXP?

Once they die and reborn, when they appear and you are sending packets they die. Not time, after time, after time.

so if you were to record a whole game and play it back would that work?

you might be able to record the packet that you send the to "auth" servers to update your level, haven't tried that as of yet. But finding that packet could be a pain in the ass.

lol yeah i guess

You don't send an "I killed you" packet, you send an "I shot you" packet and then the game decides if the person dies. If you send the packet repeatedly, it still won't rack up 10 billion kills, because the person won't take any damage until they respawn. Plus, they leave after a while.

the best way is always to try.