It usually works fine. I swapped in my Verizon sim when I arrived stateside and could only connect to Verizon 3G until a network reset. The Verizon LTE apn may not have populated when I swapped my sim back in. Verizon's sim deactivates the edit apn menu.

You may need to edit the foreign sim apn's to get 3G/LTE service. I like to look this up ahead of time and keep it cached locally on my phone in case it is needed.
https://support.apple.com/en-us/HT201699