The backup/restore(migration) is possible between different platforms like 4270 and 4280, as long as both the appliances are on the same version of OS.
The process(migration) is mentioned in our Installation Guides.
https://support.riverbed.com/bin/support/download?did=52mm6ahgcl1bghf91o9a35qiim&version=10.22
Migration of the Netprofiler 4270 to Netprofiler 4280
Kindly refer page no:29