Can you interchange all types of seats between minis? i.e. if a vinyl seat owner wanted cloth sport seats, or leather seats? Or new color?

 

yes

 

Didn't they change something in the 05s for the advanced airbags with the passenger seat detecting the weight ?

 

yes, but you can still fit the seat into an older model. You can take the part in or out of the seat in question and just swap it by pulling the cover off the seats.

Same goes for seats that were heated etc. I had heated, replaced with non-heated seats, and just recently switched the heating sections on them as I made my old seats into office chairs.