I've been refilling the 1lb propane bottles for the last few hunting seasons and haven't had any issues to speak of. I will stick the small bottles in the freezer for a couple of hours and bring the 20lb bottles inside the shop and allowing them to reach "room temperature" before connecting the two with the larger bottle upside down. I found doing it this way allows you to better monitor the fill of the smaller bottles (the warmer gas creates a condensation ring on the colder 1lb bottle).

I have noticed some ballooning or bulging in a few of the 1lb bottles I've refilled before so do have some concern that refilling multiple times may impact the integrity of the bottles.

I could be completely wrong in my thoughts, but I'm not sure you can technically overfill the bottles as you're essentially "leveling" a set volume of gas between the two bottles. Am I thinking through that accurately??