I didn't write the OP you're responding too but I think he just means make it last, not literally stretch it lol
Yes, virgin muscle is muscle that has not acclimated to the regular pinning process yet.
I wouldn't mix carrier oils as they have different viscosities and shelf lives but I think technically it's safe? (someone correct me if I'm wrong).
You could fill the syringe but that would be a pain in the ass to do every time you need to pin something. Best practice is to mix a fixed amount in another 3rd vial, heat that vial to ensure proper mixing then draw from the newly diluted solution.
For example. Lets say you have primo 200 mg/mL and you can tolerate it and want to make it primo 100 mg/mL. You take an empty 10 mL vial, draw up 5 mL of the primo 200, transfer it to the empty vial. Now draw 5 mL of sterile MCT oil and transfer to the vial with primo 200 in it. Now heat the vial and swirl it around. Congratulations, you now have 10 mL of primo 100 mg/mL
Hope that's explained clearly enough. CHeers.