Yeah I noticed that if you edit any memory while playing Multiplayer you get banned from that server forever so stay SP to edit then go legit for Multiplayer.
unfortunately, i think this is the main reason we will not be seeing a terraria trainer, since it is too easy to abuse for multiplayer.
It would be nice if there was a middle ground, but there really isnt one, because SP characters and their entire inventories can be used multiplayer.
id like to be proven wrong though.