Footprint to accomodate chips with different pin count
The way to do this is commonly done with variants, but you have to produce two design files, you can use the same schematics and output two different designs (boms or PCB's). This also helps with manufacturing because you only send one set of files to the manufacturer and this creates less confusion.
For example:
I have boards with parts that use the same PCB, but have different parts loaded for the same component, I use variants to keep track of the parts and create two different BOMS's. I then keep all the files in the same zip folder and create two zip folders for each variant. When I want to order I send the correct zip file to the assembler and they build that design.
The different pin count might be tricky with a variant but doable.