I dont think it really matters about the Proviron.....but i think that you would beta more even release if you split them up.......Something that worked for me with the prop (but it still usually hurt like shit) was hold the vial in my hands to warm up the liquid with my body temp. Thenrelaxed my muscle, rubbed it, injected slowly, then massaged the injection site. It helped sometimes, but not always.
50mg is good dosing for proviron, its halflife is about 13hrs, so yeah, you need to split it up... 8am 8pm or something similar depending on your schedule.
Prop pain is another story, there are many different reasons to get it, and each one has thier own cure, sometimes it helps, sometimes it doesnt.
You dont want to heat the actual needle or anything, but you can run the whole syringe under some hot water, to get it up to body temp, and that sometimes helps some. Also, you can cut the prop with sterile oil, that sometimes helps. The big thing is massaging the area after you inject. Not one of those little wimpy push on the area for 30 seconds, either... deep tissue for at LEAST 3-5mins... does wonders. Also, a heating pad afterwards helps some. You can always try using ALL of these things together, and it should greatly increase your prop experience. And the final thing... get different prop... some hurts like hell, some doesnt... my homebrew is almost painless.