Eh it's not really something that is coached, sometimes there is just a miscommunication out there, for example perhaps it looks like the guy you're replacing is coming to the bench so you start to hop on, and then he changes directions. Or sometimes it seems like a good time to change but then the play develops differently than what you or the player you are changing with expected, and now the puck ends up somewhere that makes it a bad time to change and both players aren't on the same page. Unfortunately these things happen. Benching someone when there's a too many men penalty just isn't effective or a realistic expectation. Might as well bench anyone who takes a hooking penalty. Also one thing that I never see anyone mention is that these too many men penalties happen because line changes are done very quickly so as to minimize the amount of time your team is defensively vulnerable, so while you could eliminate these penalties by changing slower, it's hard to quantify how many more scoring chances are yielded by not pushing the limit on the changes. Now of course I don't expect anyone to just be okay with taking too many men penalties, but I think it's good to keep in mind that the other end of the spectrum is changing too slowly and giving up odd-man rushes.
Also this idea that having a big tough guy would deter opponents from throwing big hits on the Devils seems to contradict your notion that they should go after Trouba. Well if big hitters are really so intimidating that they deter hits, then wouldn't everyone be afraid to throw a big hit on a Ranger, including Trouba? Also, ask a Leafs fan if they think Ryan Reaves has been a worthwhile use of a roster spot. He sure didn't deter Brad Marchand from sending Timothy Liljegren flying feet first into the boards and onto LTIR, and on top of that he is yet to record a point this season and is already a -11. I wouldn't be surprised if he gets waived before the season ends.
More importantly though, sorry to hear about your health issues and losing your mom. That's a rough few months. I hope you make a quick and full recovery.