When to change

I am Newcastle as have just started and my team are playing very well with the 4-3-3 formation with Carroll up front by himself

Eventully after by my own players and buidling them into a team I want to play a 4-4-2 with 2 good strikers !

But when do I change ?

Put a 442 formation into your second tactic slot and let your players slowly learn it, when they are fully 'blue' with all areas of the tactic start using it. No point in swapping a winning tactic for one your team is unfamiliar with.

I always play as newcastle and use 442. However, 443 then 442 is possible and a few indicators will be what you coaches preffered formations are and your players preffered postions.. You could use 442 in minor games or ones that you think you have a chance of winning. In real life nufc seem to play better 442, dreadful if 451 (mostly) and use 443 when chasing the game.

I found that Nile Ranger. especially in the 2nd season, starts to come on leaps and bounds if you give him first team experience.

Good luck with your experimentations.