Worth trying to upgrade RTM with PartyPack Ultimate?

The Signature Edition shouldn't have any "extras" outside of the packaging. Too many things that can go wrong if they alter the software. It should be 100% identical.

You'd have to make your own .iso to perform a direct hash check, and in that process you're not going to compile it exactly 100% the way they did. I wouldn't even bother.

I'd assume the signature edition is RTM (Ultimate) exactly, and you shouldn't need to reinstall or anything. Just enter and activate the key.

I think the main reference is the KEY. I am sure I read that the KEY for the new VERSION is UPGRADE Version. and since he installed the RTM as CLEAN install, NO he can not simply use the UPGRADE KEY to make the CLEAN install activated.
He can insert the UPGRAGE disk, and chose upgrade, then when ask insert the UPGRADE KEY, and it will upgrade and ACTIVATE when he choses the ACTIVATE NOW.

The upgrade key is not a clean install key.... It only works on a upgrade.

That is why i showed my Special Edition Signature Version.
IT WAS AN UPGRADE VERSION. NOT A RETAIL VERSION.

If the party pack version he gets is RETAIL and not UPGRADE, then he can simply insert the RETAIL Key and Active if he installed with a RETAIL Version, and the version he installed is actual RTM - 7600.