TMobile line as secondary eSIM

I opened up an account on Tmobile after trying out free data on my unlocked Verizon iPhone 13 as secondary eSIM. It worked great, so now I have a Tmobile line too on iPhone 15. I am guessing I can add Tmobile line again to my Verizon as secondary eSIM, but what happens to iPhone 15 when I do that? Another question is, is it possible to switch the two iPhones around if I wanted? Will it cancel line out if I activate the phone on Verizon? They are both unlocked phones with no payments. Thanks.