I understand your point and thats a good point you got there, but i partially agree that would be even a problem.
Lets think in the new player perspective (because this specific group of player will be the most affected for not knowing the command). Assuming they know about they can hunt a STA with a specifc ID from a specific Mob (in this case shamb) and they don't have enough gear to solo it, they would have:
1) Have the correct ID to get the drop, so they make a room and wait for other people to help him;
2) They would have to join a made room;
In the first case, assuming 3 players join his room, it has a great chance of one of them to explain him that he could turn on/off the green names and that turning off, would raise the odds of getting the drop. This is most likely to happen cause or people bitch when someone is not doing things optimal (for example shared drops) or people like me that simply like to help and teach stuff to newbies (cause i suffered from not knowing the /bank command for like a month, because nobody teached me that command existed. I only discovered it cause i wanted to xfer a varista from my hucast to my ramar and asked a guy in the lobby to help me doing it and he kindly explained me about /bank and other commands).
The second case is similar to the first, but also has a chance of a more experinced player that already turned off the green names.
So either way, the player will not get through all event without learning the command. This considering that he plays regulary. Of course it could be annoying as you correctly stated, but i don't even think it should even be considered, cause its not harmfull.
More specificly about the drop rates ajustment, imo a 1/200 ish drop rate for STA, like last year iirc, i think its hard enough, with or without green names and shouldn't be subject of adjustment. I don't even think in this particular case, should even use the rare monsters appearence as a "parameter" to choose the droprate. Thats my opinion, but can be unfair, since i don't do droptables, so i really don't know how its your philosophy when making droptables.
No change is bullet proof in all the possible cases, but overall i don't see any major problem with a command like that and the consideration about raising the drop rate on a specific drop, having this command implemented, should never be considered.
I think the idea is great, but i don't think it's a must have thou.