Okay I have a weird question here that is more roleplay-related.
According that the Galactic Empire is an ''evil'' faction and the NR the goods guys, is it legal ( or acceptable ) if one day, a new Emperor leads the GE and just decide to reform the faction's morale. He or she decide that now the GE stands on justice and equality morale. Could it be acceptable that one day a weird scenario as this happens in the combine ? or we have to mostly stays in the roots of the movies ?
another example could be the New Republic new leader decides to kill billions of innoncents and starts causing chaos in the Galaxy....
Actually, from an RP stand point, the Galactic Empire is no more "evil" than the New Republic is "good". It's all a matter of which side of the playing field you are looking from, or if you are simply a spectator in the stands, and how you choose to interact with them. As for the Combine's relation to the Star Wars movie roots, we have deviated from that long ago (SWC Timeline). We've been doing our own thing for many, many years. Remember, we have an Alderaan!
As for the hypothetical examples you gave. Interesting, but most likely doubtful to happen.
The GE is not inherently evil, nor is the RA/NR inherently good. Each side is "good" from their own perspective, and often from the galaxy at large. I myself would not consider the NR any better than the GE currently.