Hi,
You're approach for replacing a N5996UP chassis is definetly valid.
With regards to your question on the License transfer, you can transfer the license by using the Product License Registration Tool
https://tools.cisco.com/SWIFT/LicensingUI/Quickstart
Start the license wizard and a new .lic will be generated by the system.
Alternativly you can open a TAC case to rehost you license files.
Regards,
Kristof