OK, thanks. I don't have access to those manuals so can't comment. But I do have access to the MLB rules, as follows:
3.07
The umpire-in-chief, after having been notified, shall immediately announce, or
cause to be announced, each substitution.
3.08
(a) If no announcement of a substitution is made, the substitute shall be considered as
having entered the game when—
(1) If a pitcher, he takes his place on the pitcher’s plate;
(2) If a batter, he takes his place in the batter’s box;
(3) If a fielder, he reaches the position usually occupied by the fielder he has
replaced, and play commences;
(4) If a runner, he takes the place of the runner he has replaced.
How many times have we seen the situation where a potential pinch hitter gets loose in the on-deck circle. Team on defense waits until that player is announced before possibly making a pitching change to get a lefty-lefty or righty-righty match up, or whatever. If the defense made a pitching change before the potential pinch hitter was announced, the offensive team could sit him down and send the original hitter or another pinch hitter up, without losing game eligibility for the original potential pinch hitter.
Using this analogy I do not see why a potential relief pitcher who has not been announced and has not even stepped on the field or on the "pitcher's plate" must enter the game.
Again, without seeing the manuals can't say if what happened in the Mariners-Red Sox game was a bad rule or a bad call. All I know is that it was bad.