ehh, no there's no such thing as "upgrade hack".
the client is just displaying what the server says. there's no way for the client to dictate the outcome of a server calculation.
client sends a message UPGRADE_REQ
server responds with UPGRADE_ACK
then client sends (when you click the upgrade btn) UPGRADE_START
server responds with UPGRADE_RESULT
theres no client logic in between. it doesnt even send the item index. it sends your items location in your inventory (inventory slots are not a 2d matrix, they're labelled from 1 to 250 from top left to bottom right) as well as whether you used a rate booster (that's a flag) and its location.
I dont remember the structure of the response packet but it's probably a success + new item index.
the closest thing to an upgrade hack I guess would be to upgrade your item, and if it fails immidiately crash the server before it saves your result in the db (it does it every few minutes, depends on how they configured it, it could be 60 seconds).
but I'm not gonna tell you how :)