But you can’t put the blessings you want on it without having those blessings, and in the old system that means spending materials (aka time) to RNG gamble for them. And the RNG can be downright brutal.
In the new system, you’ll still be able to pick up a weapon on Melk or the Req shop or RNG gamble at Brunt and upgrade via consecration (confirmed in the first Itemization Q&A).
Then you’ll have to use that weapon for some amount of time – that is, assuming we’re talking about weapons we’ve never used before and not ones we have blessings for, which will shortcut Mastery progression for existing players – to be able to swap in whatever blessings you want.