United began their pre-season tour of the United States with a comfortable 5-2 win over LA Galaxy.
Mourinho deployed a back three for the match at the StubHub Center on Saturday.
"We are not going to repeat in the next match the experience [of LA Galaxy], so players [will be] playing in different positions and thinking football in a different way, and being organised in a different way," the Portuguese told MUTV.
"We are also going to play with four at the back.
"We will work with the same principle - 45 and 45 [minutes] and, if there is a chance to give five or 10 minutes to another kid, it's always good for them."