OK to switch back and forth between vaginal Premarin cream and Estradiol cream?

Hello everyone, and thank you for all the AMAZING information I am finding here. I just started using Premarin cream for persistent urge to urinate - yes I know how it's made and not loving it, but it's not the point here. The pharmacy just informed me today that they are having problems with the refill due to some supply issues, so I am considering getting a script for estradiol. Does anyone have any experience switching between the two, or even going back and forth based on the availability? I assume that it would not be like starting over and the benefits would be retained? I am already on CombiPatch for about two years, but had no idea that my persistent urge to urinate may need to be addressed with additional topical estrogen, until I found this information here, so Thank you!!