iMessage groups when changing SIMs and phone numbers

Hello,

I will be travelling outside of my country for a couple of months. I will be getting a local sim (international) for the country I am travelling to. However I had a question: when I change my SIM card, will the groups still be visible and will I still be able to send messages on them? Some of my friends who are there in these groups also travelled and got local sims, and it showed '(international number) added (international number)' to the chat in the log, with both numbers being the same local international sim of the friend. This international number was not originally in the chat and essentially added itself. Does this mean that iMessage automatically detects your new phone number and adds that to the groupchat, or is there something I need to do with iMessage settings before putting in my international sim?

Thank you