Hello,

I own about half of larian games in physical format, and it would be really cool if I could add them to the larian vault.
For example I added Diablo 2 to my Blizzard account today, even if my Lord of Destruction CD is buggy.
They only asked for the CD-Key (which I obviously still had).

So, can you do this on the larian vault too or is it impossible ?

It may not be impossible, but the DRM was removed from most of the earlier games, and some that used CD keys had the code on the disk itself, rather than being typed in. This would make verification unreliable, and (more importantly) a manual process.

Also, the store function of the Larian Vault site was removed after changes to the tax laws in the EU (for digital goods) in early 2015, which meant it was no longer possible to generate voucher codes (which resulted in the end of the upgrade offer for Divinity 2 Developer's Cut, for those who had the D2:ED/DKS retail release, or a digital version that didn't participate in the upgrade program). That functionality would need to be added back to the site.