> See above. I'm maintaining a FAI setup tree for production use and > won't take the risk to break something.
You can have several, independend FAI setup tree! Several ways are possible *) use the -c option to make-fai-nfsroot and a completely different fai fai config and nfsroot directory *) use a different machine for the test-FAI and let your DHCP-Server serve a different root-path for those machines that you test with FAI.