Yes, but I usually sand it lightly first.
Paint can be applied over varnish, but it needs to be a compatible type of paint for the type of varnish, and the surface needs to be prepared by removing loose material, dirt and sanding. If it is not a compatible paint the surface needs to be etch primed. Contact a local paint supplier for advice.
That is not generally recommended.
Usually yes. You'd be advised to use a water based varnish, and rough up the paint a little before coating.
You can but you will want to give the vaneer a light sanding first.
You could use a clear varnish.
You can paint over the letters with a clear nail varnish, just make sure you don't get nail varnish all over your keyboard.
For oil paintings: best let it dry for a longer time (6 months or so), then put dammar varnish over it. The long drying time makes sure you can take off the varnish later, without harming the paint itself.
Yes, you can. Use workable fixative or retouch varnish.
It will protect the paint as long as you use a water based varnish, never use oil based varnish over water based paint. Tip: "water based enamel= water based finish". "oil based enamel= oil based finish".
theres 2 ways you can lightly sand over it. it give the paint some texture to hold on too. are you can kilt over it and that will allow you to paint over it
If the varnish hasn't already dried, I'm afraid the only way to conceal it will be to paint over it. If it hasn't, wipe it up quickly.
Start with a primer, Perma Seal is great. then I would use oil based paint.