counter point though. a majorly changed Falcon in Solo would require a new (equally expensive) Falcon mockup for filming. why bother with that though, if they can use the existing one, and just stick a different dish on the one they have?
my guess is that if there are changes, they'll be mostly internal.. a new cockpit interior (closer to the ANH look) set, some modifications to the 'hallways and rooms' set, etc.
this would maximize their ability to use existing expensive mockups, and thus free up budget for any wholly new ships they need to build exterior mockups for.