That's buIIsh!t! I do change my formation before every match. You only need to keep morale high and use proper counter formation and tactics.
My last season resuts: CL 3rd place, League 2nd place (wasn't first because 1st team had better goal difference) Cup Winner!
I've played against teams that were afraid to change formation and kicked them out of the competition.
Predictable opponent is easy opponent.
"If you know the opponent and know yourself, you need not fear the result of a hundred matches." Sun Tzu adapted
You have way more chances with 4-5-1V/4-1-4-1 than with 5-3-2