American phone number no longer messageable on my iPhone XR while traveling, any way to change this?

If you have an international SIM in your iPhone, then your American phone number is not going to work on that device. You should be able to receive iMessages with your Apple ID if that is configured as a send/receive option for iMessages. You need to confirm the status of your iMessage on that phone after you put in the international SIM. What happens if you try to send an iMessage with this international SIM? Do you have cellular data? You should be able to send an iMessage with your Apple ID, but since you have associated your iPhone with the international SIM, that phone is using that number, not your American number. Only one phone can have a phone number associated with it, that is how the IMEI that identifies your phone to the cellular networks works. If you wish to use your American number, you need to take out the international SIM and activate your phone with your American number again. You need to have people message you with your Apple ID in this case.

You can't use iMessage/FaceTime without an Apple ID.