I think it really depends on the relationship you have with your assignor. I had a JVB upgraded to a
VB yesterday by my secondary assignor. My primary assignor called about 10:30 last night to see what I had that night. He thanked me and then about half an hour ago, he called wondering if I could do a DH tonight as he had someone back out. I will leave earlier and know that I am with a rookie, but I don't mind giving back as I had received earlier in my career. This assignor has been very good to me and the only turn backs I have had were due to a death in the family and leaving for a business trip early in the morning. That was a 10 pm game, so he understood.
I have had other situations when an opportunity to get a
VB game and turning back a JV game was met with vitriol. But, if you have a good relationship built up with the assignor, you can work through things.