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Those chlorine tablets contain sodium hypochlorite. I have experienced a rust colored stain on my pool wall comming from the skimmer shelf where I like to place them. Hard water would not concentrate in one location forming a rust spot. You can try sanding them with wetsanding paper. The amount of plaster removed will not require refinishing.
As for resurfacing alternates to replastering, epoxy is the only alternative I have heard of. I have worked with epoxies in many applications over the years. I do not recommend doing it yourself. It takes a crew performing multiple tasks all at the same time, and specialized equipment to apply the epoxy evenly. Epoxy, as a rule, is succeptable to breakdown by UV from sun exposure. A manufacturer of resins, which I use frequently, does produce a clear tabletop epoxy with an unkown additive to resist UV damage. I expect this additive must be used in the pool epoxy applications. It is definately something you want to discuss with your applicator and get something in writing that the coating is unaffected by UV.
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The rebar would need to be subjected oxygen or an oxidizer like SodiumHypoChlorate. There would need to be a visable crack to let fresh and sufficient quantities to attack the iron. As the iron is oxidized it expands, fracturing the cement even further. Rust is a permissable coating on rebar, by code. This is because it's oxygen supply is cut off once it is embedded in concrete. In that state it can rust no further and will not explode. Once rust has begun, and has an oxygen supply, it can only be halted by removing the rust with phosphoric acid. So here's what to do. Dig a 2 foot square hole beside the pool. Did to the depth of the bottom. Place a sump pump in the hole and make sure the discharge is as far away from the pool as you can get it, and downhill of the pool. This will prevent the pool from popping out of the ground while empty. Next get a diamond masonry blade- 4 inch for a grinder will do. Cut the crack open as wide as you have to to get to the rusted rebar. Hammer the concrete away with a demolition hammer. Abrade the rusted rebar with a grinder and wire wheel. Coat the rebar with phosphoric acid- it is commonly sold as rust remover/preventer. Scrub the rebar. Wire brush again. Vacume all dust and debris. Undercut the top of the edges of your hole. Install 2 and 3 quarter inch tapcons at varying angles as pins to help hold the patch. The more the merrier. Vac the hole again. Wash the hole and vac out the water. Mix up some hydraulic cement and pack the hole, poking to remove any voids or air entrapment. Leave 1 quarter inch below the finished pool bottom to skim the patch with Marcite.
Unfortunately the rust will have traveled some distance, and it is unlikely that you will get all of it. But if you seal it such that it no longer has an oxygen source, it should remain stable and not explode any further.
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