There is a place on the Tableau site (or maybe in the salesforce portal) that gives you the details that IT would need to build a custom package installer. As for the key, usually larger organizations use a Master Key and just embed that in the custom installer. I know if you have multiple versions installed both use the same key, it just makes you re-register I believe. Perhaps it would work if you first installed 9.3 and then removed 9.2 without having to re-enter the key. I'm only guessing on this one though.