Could a plan be redimensioned?

Hi there guys,
I have the plan for a speaker cabinet that i find absolutely beautiful (b112 nx)[folded horn]. I'd consider recalculating the measures for it to match a 18" or 21" driver (from a 12" driver) but I'm not sure if this change will affect the quality of the sound in any way. Looking forward to your opinions.

In some cases it's possible to scale up a design from a 12" up to an 18" or 21" driver, in most cases it's not. If you have to ask if it's possible, you're likely not aware of the many things that can go wrong, or get messed up when you do. So at this point I would either be very specific or stay clear

Cubo