Not to get in the middle of this, cuz my popcorn is delicious...
But the "authorization" we are talking about boils down to this:
Zen is SO unwaveringly good at modifying/upgrading the v2.5, that Provape has said "Ok. You're so good at it, you're the only person allowed to do this upgrade, besides us of course."
Zen still has to buy the parts, and because he's the only other one allowed to do the upgrade, he's the only one who can buy them.
And Provape gave him a bonus:
Provape has decided that any device, still under warranty, is OK to be modified by Zen, without voiding said warranty.
Soooooo..THAT is what the "authorized" part means.