Whether to "parole" a detainee ("senior" or otherwise) is a matter within the discretion of the Executive Branch, subject to Congressional action where Congress elects to take such action. As such, it is a Political Question.

Parole has been around for a long time. For a pre-9/11 look, see, 1998 Brown, Prisoner of War Parole.

In a civil war, POW questions (including parole and exchange) are complicated by the issues underlying the armed conflict. The Lieber Code of 1863 has a lengthy section (119-134) covering parole. That General Order was preceded by the 1862 Dix–Hill Cartel (Wiki and Agreement). Despite the outlines provided by these legal sources, the Chronology of the Prisoner of War Exchange and Parole Cartel amply illustrates that a "one size fits all suit" did not exist.

My view: as a general rule I'd follow Grant (snips from the Chronology link):

April 17, 1864 Grant issues orders to Butler essentially forbidding exchanges unless and until the Confederates agree to treat black troops equally with white, and agree to compensate the U.S. for the early release from parole of the Vicksburg and Port Hudson garrisons.
...
August 18, 1864 Grant writes to Butler, "It is hard on our men held in Southern prisons not to exchange them, but it is humanity to those left in the ranks to fight our battles. Every man we hold, when released on parole or otherwise, becomes an active soldier against us at once either directly or indirectly. If we commence a system of exchange which liberates all prisoners taken, we will have to fight on until the whole South is exterminated."

August 19, 1864 Grant writes to Union Secretary of State Seward, "We ought not to make a single exchange nor release a prisoner on any pretext whatever until the war closes. We have got to fight until the military power of the South is exhausted, and if we release or exchange prisoners captured it simply becomes a war of extermination."
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Oct. 1, 1864 Lee proposes an exchange with Grant, but the idea founders on the question of black troops.
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Oct. 15, 1864 Stanton places all prisoner of war issues in Grant's hands, with instructions to "take any steps that you may deem proper to effect the release and exchange of our soldiers and all loyal persons held as prisoners by the rebel authorities."
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Jan. 21, 1865 Grant informs Stanton that he has given instructions that negotiations be re-opened with a view to resuming a general exchange.
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Feb. 2, 1865 Grant informs Stanton that he intends to exchange about 3,000 men per week until one side or the other has no more prisoners. The Federals intend to exchange men from states such as Missouri and Kentucky first, to minimize the chances that they could be put back into their units.
but every rule has its exceptions ("METT-TC").

Regards

Mike