Air carrier Captain reported the runway braking action was not as reported and the aircraft required the use of reverse thrust to stop from sliding off the runway.

Narrative

On our way to ZZZ; we received a report that Runway XX had a condition code of 4 so we could expect some trouble braking. On our final approach; the Tower told us the previous landing aircraft reported the braking action to be good. On our landing roll; we also reported to breaking action to be good. However; minimal braking action was needed at this time because most of the runway turn-offs were closed. This meant we had to roll all the way to the end of the runway and use the final exit. The aircraft slowed down to about 15 kts. easily. As we approached the final exit; I applied harder braking to slow further and make the turn. The aircraft did not decelerate at all. I could feel the anti-skid system trying to gain control. I was also trying start a gentle right turn but the aircraft kept moving almost straight ahead. I determined that; at this rate of deceleration; the aircraft would run through the runway end lights so I applied max reverse thrust. The reverse thrust slowed us to about 5 kts. I was then able to continue the turn while stowing the thrust reversers and regaining braking control. The aircraft came within 10 feet of runway end lights before regaining control. I am writing this report because; per our company policies; use of maximum reverse thrust is prohibited at speeds below 75 kts. After turning off the runway; we asked Tower to amend our braking action report to medium to poor. After shutting down the aircraft; I informed one of our chief pilots about the incident. He told me that the aforementioned policy is most likely just a company policy and not an aircraft limitation; but I should check with maintenance. I checked with maintenance and they agreed.More accurate braking reports; as well as; better runway plowing would have helped this situation.