Can a soldier move to a different crew when is capo is active !
And who decide that ? Only The boss right ?

Most prominent example is probably Sammy the Bull' from Shorty Speros crew to Toddo Aurellos....

Wait, did you mean just crews, or families?

Crews

I was under the impression that this has happened or happens from time to time.

sammy gravano was just an associate not a soldier at that time
he was with the colombo's at first and he went to the gambino's after a meeting

Lefty Ruggerio was in a different crew but moved to Sonny Black's crew after Carmine Galante was whacked. Not sure what crew he was in originally.

Interesting question.

It would definitely happen if the captain died or was shelved or something because that crew would be taken over by another guy or shifted into another crew.

But does it ever happen where the soldier moves without anything happening to his capo?

Definitely can happen. If you read the Scarpa FBI files, guys were being moved around crews all the time.

Also, Al D'Arco says that Mike Pappadio was moved from his old crew (East Harlem/Bronx presumably) to D'Arco's crew so he could be watched better.

there is any reason for why they switch crews ? does the capo ask for it or them ?

I believe Lefty was with Mike Sabella before Sonny Black

Napolitano was also in Sabella's crew, and picked up the captain spot when Sabella was knocked down. I think Napolitano offered Lefty a spot in another crew if there were hard feelings about Sabella, but made it clear he wanted him.

I don't know the exact circumstances, but I believe Scarfo sr. was moved from Skinny Razor to Freddy Iezzi's crew way back in the day..I'm not sure about this so don't hold me on it..just my 2 cents..

Thanks !
Btw you have great posts !