Yeah you can mix it just fine my man. It's been years but I used to do that quite often.
I had a friend that'd grab hard as the soft that was around was never as good.
He would cook back the crack for quality purposes.
Then take the cookback prep with vinegar & throw in some dillies or heroin for good measure.
Then each of us would suck up an = number of units with a clean rig & away we'd go.
So you should be good to go. Assuming your talking east coast dope not black tar.
If your talking black tar I'm not familiar. But I assume it would work just as well.
You would just have to prep the black tar however it's prepped & mix it with the crack/vinegar mix.
Can also use other acids such as lemon or lime juice but they can have a fungus that fucks your eyes
so your best off with the vinegar. Burns like a bitch if ya miss till the crack numbs it though.

Ah the memories, could go for a nice speedball right about now myself. Enjoy!