There's a lot more to it than just putting in the new controllers. Most customers will get Partner or NetApp PS for the headswap.
Edit: there are two ways to do "upgrade controllers". There's the "head swap" part, which is moving disks to a new controller pair; or Volume move, which is taking a 2 node cluster and making it a 4 node cluster temporary and moving over the volumes. and converting it back to a 2 node cluster.
I've not ever done a head swap with internal disks honestly, those systems i've always moved using the vol move method.
For the A200 to A220, I don't think you'd be moving the controllers, you'd be moving the disks in to a A220 chassis/controller.