|>> Ok, is it possible to enter a different serial number during activation, than what I entered during installation? <<|
No you cant. At the time activation comes around it works on the serial number that was entered during installation and there is no opportunity to change it.
Activation is either accepted or rejected and with the same serial number on multiple copies, it will be rejected.
Theres no way round it, not legally anyway, other than having separate installations for each machine.