Iphone 12 pro esim questions

I have an Iphone 12 pro, it only holds one esim but as my understanding it can hold up to to 8 esims.

My question is the following:

If I have active an esim on my home country (USA), and then travel to China and add a second esim, i will activate my second esim in China, can i later (once return to USA) activate original esim from USA? or would i need to go to cell phone provider? Can the USA esim be left in hold while i activate second esim, and when return to USA activate original esim? Please comment