Ok zozo;
Downchanges:
What you described is bad for the: clutch, gears themselves, syncomesh, engine and drivetrain generally.
Basically if you can feel an underbrakes downchange then you did it wrong. You should either not change down until wheel speed is suitable (eg soming up to traffic lights) or you should rev-match by heel-toeing (eg whilst cornering).
The message: You have brakes for a reason use them - gears are for accelerating not braking. (only exceptions being cases of brake failure and steep winding descents).
Headlights:
Cars do not short circuit if you start them with the headlights on.