My understanding is that the rule was set for the 2018 season such that a team could not use the replay room to decode the signs as the game was in progress. You could use prior tapes or after the game was over you could. That is the distinction as i understand it. Since the replay room has to be able to communicate with the dugout for the purpose of questioning umpires calls, the means of communication was set up in advance. A person could just as easily go between the two to communicate as well. Clearly the temptation is there to decode the signs during the game, since the same guy is allowed to do that before and after. My understanding was that a hitter who got to second could then use the information and relay it to the player at the plate. No banging of trash cans and no buzzers worn beneath the uniform. Also, easily defeated by changing signs with a player on second.
I'd bet that other clubs have done the same or similar things so a harsh punishment is neither warranted or fair, unless Manfred wants to open the investigation to other teams, such as the Yankees. Probably the rule should be looked at, since it is hard to enforce and not importants, since teams can avoid any harm by just changing signs. I have no information about the Yankees or any other club using similar sign stealing as the Sox used, but it is quite likely that they did.