So you think it's the right thing to to do in terms of maintaining team morale and discipline to play a goalkeeper in every round of a cup competition and then replace him for the final. What do you think the rest of his team mates would feel about that and what do you think would be the effect on their mentality for that game. What do you think would be the effect on the mind of the goalkeeper he was replaced by, who would know what the rest of his team mates were thinking. IMO opinion their sympathies would be with the original goalkeeper and it would affect how they approached that game. Players while being professional sportsmen are also human beings with emotions allegiances and friendships within the squad and club, knock these and you diminish the playing capacity of the whole team.
The leadership of men isn't a science. It cannot be taught. It is something that is innate to certain people. It involves loyalty and trust and it involves doing the right thing by your colleagues and underlings and not necessarily taking the most expedient route. This is why history is littered with battles that have been won against obviously overwhelming odds and leaders that have risen to rule vast empires by leading nomads and peasants to destroy the biggest and most well equipped armies.
Back to football. This is the reason that certain managers have the knack of taking mediocre players and making them perform like world beaters. It is done by carrying people with you and making them believe that they are valued and have a stake in the enterprise at hand. Not shitting on them at the first opportunity for some perceived short term benefit.
We have seen both approaches in action, the 2013 FA Cup final where Pantillimon was replaced by Hart for the final and the 2016 League Cup final where a better man manager stuck to his principles and did the right thing by one of his players.
I'll let you draw your own conclusions.