I have a question about text messages and changing sim and carrier. Will they stay on my phone, or will I lose everything ?

Hello.

I will be moving country next month, and will change to a local carrier.

I was wondering if all the chats and messages with my contacts will remain or disappear.

Also, connected with this, I will be changing the location on my Apple products, so that I can access local apps - does that make my current country specific apps invalid or may I continue to use them ?

Many thanks.