You absolutely can mix your compounds, id rather do one injection into one site and mix the oils, I just did a shot of test and primo today zero pip, primo has come a long way and labs have figured out how to minimize pip if you get quality primo.
I've run primo and test for 2 cycle straight, if u have issues you can run the barrel under hot water for a few minutes and shake it to mix the oils together, it will cujt down on pip, just make sure the syringe part has the plastic cap on it while u do it.