Replace old entrance door - How to install a new one?

I don't quite understand the question. The new frame is then 20mm wider inside and outside. This results in a chain reaction of rework. Floor, insulation, wood paneling, plaster, paint, floor edge profile, etc. I would clearly just go back to 70mm here or simply have someone check whether the existing door can be adjusted. It's not that old. I wouldn't bother without first clarifying whether it can be properly adjusted again.