Hello! I'm on the exact same situation, but, my environment is Odoo 16.3 saas, so I dont have the option to install 3rd party apps. 

I want to have a slip and record a serial number when I receive from my customer, in some cases I can repair the item and send back the same serial number, but in other cases I deliver a replacement with a diferente serial number, so I want to know if this is possible in standard with saas.

Thanks in advance for your help.

Hi,
There are third-party apps available- https://apps.odoo.com/apps/modules/15.0/repair_stock_move/,
You can check this module is functioning as expected.

Hope it helps.