Yes, you can.
Apply a coat of exterior paint over the interior paint to protect the finish and to discourage mildew growth on the paint film.
As long as you are using a similar type of paint (I expect it is an indoor latex, since baseboards are found indoors) and as long as the existing paint is still in good condition and is not flaking off, then yes, you can paint right over the existing paint. If the paint is in bad condition, you should remove it before repainting.
I believe that you prime than paint than seal. It depends on the paint you are using and what you are painting A lot of the exterior paints used today don't require any undercoat. However if you are painting over a previously painted surface you must keep preparation in mind.
yes, I think.
Yes, oil based paint is very versatile and can be painted over many painted surfaces, including those previously coated with latex paint, as long as the surface is dull and clean.
Exterior Acrylic paints are NOT acceptable over PVC vinyls (Duradek) Adhesion is suspect at best, as well as color retension is poor especially in dark colors
Clear primer.
You shouldn't. Primers are made to adhere to a surface and/or bind loose particles. Interior paint, and some exterior paints for that matter, could easily become detached from wood and stucco over time and won't hold back tannin stains on wood. If you are painting over a clean, sound surface that's over a month old, then you can get away with using two coats of 100% acrylic exterior paint.
he painted over 2000 paintings
Yes it can.
The short answer is yes. If they are both of the same base (latex, oil, acrylic).More important how ever is where the paint is. If you are working out of doors, go right ahead, if however you are intending to paint an exterior paint over interior paint, indoors, then please do not do it.Exterior paints have a number of chemicals that make them more suitable to exterior conditions, and a lot of them are not good for you. The out-gassing process takes a lot longer and exposes you to potential harm.
Yes. Still follow the rule of "Never apply a coat of paint onto anything powdery or starting to flake off." If that is the case you will need to prep the surface first. Probably by sanding it.