Well, here is the scoop; someday you will replace those water lines, it is inevitable. That system you are talking of would probably clog them up for good. That epoxy is mainly used for copper piping and most times they won't discuss what happens when there is a total blowout of the copper tubing in the wall or ceiling (they have to go in and replace a section like you would any other type of piping) and this is what you are trying to avoid to begin with.
As with any water line system in a home there will be removal/patching of walls/ceilings/floor depending on the areas affected. In galvanized systems usually the last 3 fittings leading to the fixture usually clog up, cleaning/removing them would probably restore flow that is sufficient to operate the fixtures. Most galvanized vertical lines remain clear. Funky tasting water is probably flux; that can be avoided by proper installation without excess flux. Majority of people have full time jobs so your time spent would be around work. Do a section at a time, always connect to dielectric unions when reconnecting to galvanized until it is all removed.
Do not flux up a run of pipe/fittings and not solder the connections right away. This can cause quality issues with the solder joints. I cannot figure out why people do this to begin with.
If cost is a issue, I advise inspecting the last 3 fittings leading to the faucet/fixture; you'll see that they will be clogged most times.