How to Enter a New Final Cut Pro Serial Number

for OS X 10.6.8 Snow Leopard Systems - 
click on your MAC internal hard drive, and navigate to -
/library/application support/ProApps
find the file called -
Final Cut Studio System ID file, and delete it.
when you open up Final Cut Pro again, it will ask you for a new (legal) serial number.

For OS X 10.8.2 Mountain Lion Systems - 
click on your Mac internal hard drive, and navigate to - 
library/application support/ProApps
delete ProAppsSystemID
delete FinalCutStudioSystemID

navigate to -

restart your computer.  Launch FCP, and enter the new serial #.