looking for research advice

And fromhttp://en.wikipedia.org/wiki/Galvanized_Yankees
"In October 1864 John G. O'Neill, colonel of the 10th Tennessee Regiment,[n 4] was assigned to recruit Union prisoners to replenish the depleted ranks of the regiment. O'Neill, recovering from wounds received at the Battle of Resaca, appears to have delegated part of the task to a former officer of his company, Michael Burke. In October and November 1864 O'Neill and Burke enlisted more than 250 soldiers of a number of Union regiments from among prisoners held at Andersonville and Millen, Georgia. The recruits were required to take an oath of allegiance to the Confederacy, and were not issued arms or ammunition until the night before their first engagement.[3]
Although held under strict camp guard, they were sent to Mobile, Alabama while the remainder of the 10th Tennessee advanced to the Battle of Franklin. Organized as "Burke's Battalion" of the 10th Tennessee, they were made part of ad hoc force assembled by Col. William W. Wier and sent by train towards Tupelo, Mississippi to repel a raid along the Mobile and Ohio Railroad by two brigades of Union cavalry under the command of Brig. Gen. Benjamin Grierson. The Union cavalry force had already captured a substantial number of Brig. Gen. Nathan Bedford Forrest's dismounted cavalry encamped at Verona on Christmas Day. The 10th Tennessee and 17th Arkansas were sent with a battery of artillery aboard the first train to block the tracks at Egypt Station, a mile west of Aberdeen, Mississippi.[3]
On the evening of December 27, 1864, six members of Burke's Battalion deserted and made their way into the Union lines, where they reported the presence of the former prisoners and the likelihood that they would not resist any Union attack. The next morning Grierson's 1st Brigade advanced and came under fire from Confederate skirmishers. The 2nd New Jersey Cavalry responded with a charge in which it lost 74 casualties and 80 horses, but captured more than 500 prisoners, among whom were 253 former Union soldiers now in the 10th Tennessee.[3]
Grierson's prisoners were shipped by steamer to the Union prison camp at Alton, Illinois, where the claims of the "galvanized Yankees" desiring restoration to their units were investigated. The commanding general of the Department of Missouri, Major General Grenville Dodge, recommended on March 5, 1865 that all the former Union soldiers as well as a number of Confederate troops be enlisted in the U.S. Volunteers for service in the West. The recommendation was resisted by the Judge Advocate General's Office in Washington, D.C., which advocated that no clemency be granted and that the former Union soldiers be tried for desertion, citing disputed testimony over the degree of their participation in the battle at Egypt Station. Dodge's recommendation was apparently accepted, however, as the prisoners were permitted to enlist in the 5th and 6th U.S. Volunteers.[3]
O'Neill returned to Andersonville and recruited 150 more prisoners for the 10th Tennessee in January 1865, and approximately 165 more in March."

The yankee army had a high percentage of draftees and foreign mercenaries whose allegiance was possibly dubious to begin with. For a POW in squalid conditions with questionable allegiance to the government they were fighting for to change sides may have been as simple as taking off a blue coat and putting on a gray one.

Union Army Ethnic Groups.

http://en.wikipedia.org/wiki/Union_Army#Ethnic-groups

Foreigners in the Confederacy.

http://www.amazon.com/Foreigners-Confederacy-Ella-Lonn/dp/080785400X

Unionblue

The Mercenary Factor in the Creation of the Union Army

"The manpower crisis facing the Confederate armies in the spring of 1862 was a result of legislative incompetence, specifically, the Confederate Provisional Congress' foolish re-enlistment law of Dec. 11, 1861. The "bounty and furlough act" demonstrated, in the words of historian John C. Ropes, that "the difference between an army and a congeries of volunteer regiments was not appreciated." Every soldier who re-enlisted for three years or for the duration of the war was promised a bounty of $50 and a 60-day furlough. He could choose his arm of the service, and if he did not like his company, he could join a new one. Men could elect their own officers, "rewarding those who curried favor by laxity and demoting those who had enforced discipline," in the words of Douglas S. Freeman."

From my GGFs diary from Millen, GA in 1864.

"October 30th.
Our mess has had two busy weeks working in our prison home and have got quite roomy and comfortable quarters. Thanks to our rations of sweet potatoes and fresh meat many of us have been cured of scurvy. No surgeons or medicines, have thus far been given us. The cool weather is telling upon the feeble and those poorly clad. The death rate has increased to four or five per day. An unoccupied part of the camp is used for a ball ground and many games are had these sunny October days. We hear nothing of exchange and many bitter words are spoken against our government, as over again in that direction. Some two hundred and seventy-five have taken the oath to serve the Confederacy, doubtless from varying motives and intentions but to most of us no motive can justify the transaction.

From Florence, NC.
January 1st. 1865
No change for the better. No signs of exchange, and some of our poor fellows are weary and heartsick. They are taking the oath of allegiance to the Southern Confederacy, not many although the rebels are giving invitations freely coupled with promises of clothing, etc. The cold snaps multiply and little patches of ice fringe the edges of the creek, and with each cold wave one or more poor fellow gives up the fight, and in prison phraseology is “mustered out.”

www.civilwardiary.net

Freddy, Thanks for sharing your GGF's diary.