Sealing over a caulk:
Many caulks will repel a sealer and the sealer will eventually peel. Look for a caulk that is rated as "PAINTABLE". If paint can bond to the caulking, so will a sealer. However, test first to make sure a petroleum solvent based sealer does not melt the caulking. If it does melt the caulk, spraying might solve that problem.
Removing silicone caulk stains. Requires testing to confirm this will work for you.
If a silicone caulk has been used as a sealer (not a good idea) or you have spills and spots of this material to remove, it can be done. We have tested our Aldon "Premium Stripper" on one popular brand of silicone caulk and had some success, but with more work than normal.
Silicone caulk is completely different from those sealer formulations (epoxies, acrylics, etc.) normally removed with Premium Stripper. The stripper works on part of the caulk formulation enough to soften it. Using more stripper, more applications, and some agitation will soften the caulk enough to get it off.
Other types of caulking compounds, like latex and butyl should yield easier. But, you never know until you test.