I don’t see how a civilian force will significantly improve their chances.
Edit: this isn’t a video game. Civilians taking up arms makes them targets. The Russian aim is regime change, and at this time it appears that Russia will prevail. It is existential for Russia. All a civilian resistance will do is maybe slightly delay the inevitable at horrific cost. I think people should be discouraged from throwing their lives away on a lost cause. Even the Ukrainian propaganda of heroic deaths contains an understanding that there is no hope.