Mancini stunned his squad by banning music both before and after matches.
The former Inter Milan boss also put a block on the colour purple on all clothes, including training tops, and insisted on team meetings taking place at odd-numbered times.
He then told his stars get-togethers could not happen on the hour.
But Pellegrini has put an end to the ridiculous rules to make himself popular with his players, reports the Daily Star.
A club insider said: "There's a joke going around this place that United can start calling us the 'noisy neighbours again if they like, because at least now the boys can play music.
"He was unbelievably superstitious and completely lost his temper when a batch of the training bibs and jackets were purple.
"He said it was an unlucky colour and he didn't want them anywhere near the place. He also said meetings scheduled to take place at an even numbered time were unlucky, especially on the hour.
"We couldn't believe what we were hearing - at first it sounded like a wind-up but then the horrible realisation kicked in.
"As for the music ban, Mancini said the players wouldn't be able to concentrate if a song was in the background, even though our opponents had their stuff blaring out down the corridor.
"Once he had his way this place was like a morgue. We have returned to the real world at last.
"The new manager actually talks to the players and staff, which is something that didn't happen for three years under the last guy.
"Joe Hart can wear his purple jersey without fear of another fall-out, meetings can take place on the hour, and Liam Gallagher can once again be heard ringing out before kick-off."
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