Hi Ousturali,
For most scenarios, the aggregate, volume, and snapshot structure will remain intact when moving the old shelves to the new controllers. One exception is when you have snapshots that are 32-bit and the new controllers are running an ONTAP version that no longer supports 32-bit snapshots. In addition, 32-bit aggregates will need to be converted to 64-bit aggregates. Data ONTAP 8.3 and newer no longer supports 32-bit data. So how impactful this will be is determined by the current ONTAP version the data is on and what ONTAP version the new controllers are running.
Another thing to keep in mind is if you are also migrating the disks containing the root aggregate over then you will want to perform a formal upgrade of the existing data to match the ONTAP version of the new controllers. Booting a newer version of ONTAP with an older major revision of ONTAP will update the RAID and WAFL versions on every disk but the actual ONTAP kernel isn't properly upgraded resulting in a messy situation to recover to make the data accessible again. If the root disks & aggregate aren't moved over then you will have to recreate the SVM/VSERVER, shares, LIFs, and other configurations before you can access the old data.
Here is a reference document for moving a shelf to another controller:
Physically moving an aggregate composed of disks
Regards,