Part of the U.S. Government's agreement with the "galvinized Yankees" was that they would not have to fight their former comrades.
Hence, they were mostly sent west to fight Indians. Naturally this released Union soldiers then on the western frontier who could then be sent east to fight, the whole purpose of the program.
Thus "died-in-the-wool" rebels scorned these "galvinized Yanks" Given the death rates in the prisons, one can hardly blame those who joined. I live a few miles from the Confederate cemetery where the Rock Island, Ill prison camp was. About 2,000 rebs are buried there and that camp did not even open until early 1864 or slightly earlier.
A lady in Carroll County, Va married a Conf. soldier who died in E.Ky in 1862. She then married a kinsman with the same surname. He was a Conf. captured in Pickett's charge at Gettysburg. He became a galvanized Yankee. He returned home after the war.
The grave stone of this lady reads "Wife of two soldiers".