as far as I know Nebula looks at a different of things from your hardware to generate the serial. Think things like the CPU serial number (don't know the specifics).
So reinstall without changing anything in your hardware should NOT require a new license. Upgrading certain hardware parts might.
On the other hand, I once required a new license (under Windows) because I changed the drivers for my harddrive (SATA controller, changing from Windows-default to Intel's own) and suddenly my license was not working anymore . So there might always be little pitfalls.
Acustica generally don't make a big deal out of it, if you say 'I did blablabla and now I require a new license' you almost get it immediately in my experience.