Base functionality related to packages in Odoo is quite limited and would need customization to achieve your requirement.

1. Packages (Pallet) can be tracked by location, however not by specific customer

2. To make the package reusable at your company you would need to 'unpack'. Yet again 'unpack' can't be accomplished by selecting multiple packages from list view.

An alternate to managing this return process could be by having pallet as a product and defining return route

1. Create Inventory Operation - Inventory > Configuration > Operation Types. Type of operation - receipt Default source location - Partners/Customer and destination WH/Stock (or location where pallets are received)

2. Create route - Push from rule - Customer to Stock using newly created Return Operation, and make route applicable in product

3. Create Product - Pallet type consumable and inventory tab select return route

4. On your delivery order or picking operation add pallet as product. (this would be in-lieu of using 'put in pack'. Can also be added from Sale Order) on validating delivery a return operation would be created.

Also, only 1 return operation would be create per customer while aggregating the number of pallets. Validate the operation on collecting the pallets from customer

This might not meet your exact requirement and viability of this alternative is dependant on your operations and the specific way the pallets are tracked and managed.