Adrian,
1. You just can do it again (Activate).
2. On this other PC you can enter the path to the "original" PC and location (as described in here
Activation ... How ?).
3. That might be a problem, depending on what you changed on the new PC. Anyway,
in here I I also talked about that, and in the end you will always be ok.
Since it's my feeling that number 3 above must be solved by some means of automation, number 2 (I think) can be solved by the same means to avoid the awkwardness of that.
I hope this gives you a more or less good feeling.
Regards,
Peter