About Audemars piguet service

[Luv rolex]

Hello guys, Interested to know if anybody had to change their middle case in ROO before, does AP keeps the older serial number engraved on the case back OR do they change the serial by changing the case back too.

Also how did they aligned the chronograph pushers with crown on the newer 42 mm although the case is almost the same as older except the crown guards maybe.

Thanks alot