1. I think that there may be more to this than restarting the system after making a change or creating a Scan which you want to schedule.
Some others appear to have a problem and they regularly restart their systems.
2. Avast (as far as I'm aware) doesn't use skins for the UI, so no way to simply change skin. I believe the last skinable avast versions was way back in the avast 4.x era.