Not a glorified puppet, but he's going to have parameters he has to manage to. It wouldn't be anything as strict as "must always insert X pitcher to face Y Batter in 5th inning no matter who starts..." kind of s***, but more like "If X pitcher is at X number of pitches and is now in his third time through the lineup... here's 2 or 3 relief options that match up well with this part of the lineup, that part of the lineup etc. Score would obviously be a factor as would reliever availability and if a guy is on his second day in a row vs fresh. he makes decisions based on the info provided. That's not the same thing as having in game decisions made for him.
I bet that the who's in and who's out on any given day (assuming injuries arent a thing) is probably much more rigid though. Every regular is going to have planned days off, planned DH days and the non regulars are going to be platooned per matchups more often than not. They're definitely going to stick to that unless injuries force a change.