I've done it by accident before.
Bought a 4 lb. can of 4350. I was emptying a powder measure to fill it with another propellant. Dumped a bunch of Unique in it by accident.
I about died! Until I ran the numbers of exactly how much I had dumped. The percentages were like .5% of the new propellant in the jug.
Pfft! I shot all of it and didn't have any problems. Shot some nice groups too.
By all rights, I shouldn't have. But I wasn't about to toss a whole new 4 lb. can of propellant.
I joked for months about my "custom blend". I still have all my fingers and toes too.
Ed