Hoping to move to Scotland in 18 months
l am not sure on this but l don't think changing your address would be regarded as a change in your circumstances but others more knowledgeable then l would know more about this,
I don't think you would need to be reassessed if you change address, but you would need to tell the DWP because your bank details will presumably change, especially the address your bank have at the moment. 18 months is a long way away and either your circumstances or the DWP policy may have changed before then.
No changing address won't be a reason to be reassessed.