The only mixing of strings I do has to do with the scale length.
Mike Lull 35" basses are made with a through-the-body option for the B string only. All the other strings are top-load. And the B string can be top-loaded as well.
I'm not even gonna get into the top-load vs through-body string. Don't even bother. In virtually all cases, top-loading the B string is perfectly fine. However, I prefer to run the B string through the body. Because I can. But regular long-scale B strings come up a little short going through the body.
So for this reason, I order the D'addario EXL170 long-scale 4-string sets and then I order extra-long B strings. Same string family, just a little longer.