the lonestar runs in TRUE class A when you're running in the 5 watt mode. This is the only time ANY mesa amp has ever run in this mode, and the poweramp is configured in a very unique way, a way that cannot be modified into the nomad poweramp, short of building a new poweramp. the nomad runs in a typical push pull class AB, meaning that it needs a minimum of 2 tubes to put out a signal. theres alot of literature about this on mesa's website, it has to do with each tube creating one half of the frequency.
second point, the nomad 45's poweramp is unique with its dyna-watt whatithoosit, so i don;t know about fucking around. youd have to have pretty extensive knowledge of how the amp worked before you tried anything. best bet would be to use a hotplate and saveyourself the effort.
in terms of the 5 vs. 30 watt thing, their characters will be very different... infact, it won't even sound like the same amp in high saturation, although i cant say which one is nicer. the 5 watt would probably be alot smoother sounding, with a fair amount of sag and touch sensitivity. the 30 watt would probably be alot tighter, more modern. crunchier? if you own a lonestar special, just crank it up and listen.
there isnt alot of people around doing big mods to nomads, probably becuase the circuit is so complex and messy. open the thing up and have a looksy..
good luck in your search for your sound,
atleast your headed in the right direction
Andy.