You don't purchase a serial number, you set it via the config.list for clover.
Jays iMessage guide has a good explanation of setting clover and serial numbers :
http://www.tonymacx86.com/general-help/110471-jays-imessage-guide.html
Awesome, that helps to understand how to generate an S/N!!!
Now, I hope it does not sound too stupid, but maybe I missed the part in the guide, where it gets explained how you can generate all that so that it is easily combined together with the previous working config.plist which I am using already.
The reason why I ask that way is that I am worried that it could screw up the already working "config.plist"-file, by trying to get a S/N...
So, might this be the right way to get a S/N combined with the already using config.plist?
1. Run "Clover Configurator" and mount the "EFI"-Partition
2. Go to File/Import Configuration -> choose the config.plist from EFI-partition
3. Generate the S/N as described in here:
http://www.tonymacx86.com/general-help/110471-jays-imessage-guide.html
4. And click under "Generate Config" -> "Generate"
5. Finally rename the generated config (that I find on the "desktop") to "config.plist" and place it at EFI/EFI/Clover/(old .plist) by overwriting the original/old one.
Is that the right way?