You can switch back and forth between active esims by merely switching one off and another on. I do it nearly daily on my Pro Max and while testing Airalo. Where the confusion may arise is if a prepaid esim expires and has no option to renew or add credits. i imagine that is something that the issuing agent has control over when they sell a plan. Also, if you delete an esim they cannot be reused, even from a US carrier like Verizon or AT&T from what I've heard. You'll need to start over with that setup.