The opaque stains you are probably thinking about are not suitable for previously treated woodwork since they need to be absorbed into the surface of the wood for best effect.
You can use a water based gloss or satin finish over previously stained woodwork though. For a gloss you’ll need to use an acrylic undercoat first but for satin finishes just two coats will get a decent result.
The previous surface should be thoroughly washed down with a sugar soap solution, rinsed and dried to remove any traces of grease and dirt.
The relevant Sandtex products are : Rapid Dry Plus Soft Satin Paint, and Rapid Dry Plus High Gloss Paint with Rapid Dry Plus Primer Undercoat