Are you going to recreate the Appvolumes database or are you going to use the "old" Appvolumes database.
If you are going to create a new Appvolumes manager just copy the .VMDK files (hell you can even copy the entire cloudvolumes folder 
) to the new datastore, point the new manager to that datastore and select import.
All writable settings will be retained as they are attached to a user if the name of the writable is the same as the name of the user. Also, if you only attach it to a specific machine prefix name this info will also be imported because it is located in the metadata file (yes, you need to copy this as well ).
If you are not going to recreate the Appvolumes manager I'd suggest upgrading to Appvolumes 2.14 attach the new datastore to the Appvolumes manager and start moving them using the newly added feature in 2.14 of Move writable.
In the first situation you do need to reassign all appstacks though, no way to get past that.