When you "transfer ownership" it just changes the records at RA.
Your client can then either....
1. Take ownership of the activation, by re-hosting to their PC, and setting it up as an "activation server". You will then be able to "borrow" the activation while you are on your client's site.
2. Take ownership of the activation, by re-hosting to an "activation dongle" (purchase necessary). The dongle can then be used to activate any single PC to legally run one instance of the software.
3. Let you keep the activation on your PC. Wise to get it in writing that they are letting you use the activation.
You won't need to re-install any software packages, everything is done through FactoryTalk Activation Manager.
Please note that 1 Activation will only allow 1 software package to be activated at any one time to abide by the rules.