What you are proposing is a bad idea. ranging from dangerous to blooper rounds.
A little rust on the head of the case posses no problem. However, if those rounds got wet enough to rust the head of the case, it's likely the steel shot is also rusted. That IS dangerous. Steel shot that's rusted together has blown barrels of shotguns. SOME steel shot nowadays is plated to resist rust, but nothing is rust proof.
Disassembling those rounds, then using the same components is also prone to mishaps. You'd HAVE to have the exact same empty hull, the same make and type of primer, the same wad pressure, and the most important point, the same crimp. No way can you duplicate what the factory has done to assemble those shells. I guarantee you won't get everything to fit.
Loading any kind of shotshells is an exacting procedure. The recipes for reloads is not just a suggestion, but must be followed exactly. Any deviation from an exact load recipe can result is a blown up shotgun.