Can you apply a gel stain over red painted cabinet doors?
no, stain should be applied directly to bare wood. You’re going to have to sand the red paint off to apply the stain. You could however put black paint over top of the cabinets w/o sanding the old paint off. Just make sure that you know what type of paint was used so you don’t put the wrong kind on. for example: you can’t put latex based paints over top of oil based paints because the latex will bubble up and peel off as it dries.