Im so paranoid about doing that...!!
Ive done it, but only lost a small amount of powder thank god--not worth worrying about...so i used it to make a couple of rockets...
I have the powder im using in a different container...so even if i have a kilo or half kilo bottle, i tip some into another bottle & use that as the 'working bottle' & top that up as i need it...
But, i only load small stuff, & even with 308 sized cases its pretty rare for me to load more than 50 at a time, so the working bottle is only half full at most...
And as said earlier, we all know the rule---one powder type on the bench at any given time...
BTW...a random mix of trailboss & 2208, evenly sprinkled over a few overlapping sections of duct tape, then wrapped around a timber BBQ skewer & ignited, travel faster & further than one might ordinarily think...
...
The man who knows everything, doesnt really know everything...he's just stopped learning...