The question is, what to change, when to change, and how to change the stuff.
Could you give an example of how you've modified the tactic depending on your opponent and how you knew when to do it and the effect it would have?
I'll give you a couple of examples. But I have to add that these changes that I make to my tactic is not necessarily going to give the excact same effect on others. If Koflok is reading this he might have some things to add regarding the tactic he's made, that I guess you are using.
Here are some examples that I hope will give you an idea of what I mean:
Pre game:
I personally like to play more direct when 1. playing a stronger opponent, especially away. If they are a better team they probably have better central midfield players so I dont want to risk losing the ball in the middle of the field. 2. If the course is wet and the rain is pouring down I also like to play direct, rather than short passes. Be careful playing direct if there is a strong wind though.
Take a look at the opposition. Do they have a lot of players injured or suspended? Say you're playing Liverpool and they have Glen Johnson and Kelly out injured, and now they have to play their third choise full back, Wisdom, or even worse, Carragher. If Jose Enrique is playing on the left, its obviously going to be easier creating chanses attacking their right side! Then you can set your team to focus their attacks down the right hand side. If your wingers can play on either side, shift your best winger (fastest if opposition has a really slow full back) to the side you want to focus on (this should also be done during the game of course). If you saw the Tottenham - Maribor game earlier tonight, Spurs exploited the weak right side of Maribor in a brilliant fashion, especially in the first 25 minutes.
Also, you obviously have to look at the formation that they play, but this goes without saying. If they're packing their midfield, you might want to take that into consideration, the same if they're playing with focus on wing play. Look at the oppositions recent results. Take a look at the teams that have beaten them and what formations they used. They might have dropped points against weaker opposition that deployed successful tactics which exploited weaknesses.
How does your opposition usually score goals? If you're playing Stoke away, I'd say its a good bet to focus your training on defensive set pieces. If you're playing Walsall at home in the cup, focus more on attacking movement since you'll meet a very defensive team that will try to give you no room what so ever!
During the game:
First of all, its vital that you don't watch only the key highlights, since this wont give you a proper picture of whats going on with your tactic. Looking at the analysis of your assistant manger can also give you some hints!
I had a good example of tactical change during a game just now. I played Sturm Graz in the qualification round for the Europa League with my QPR. I have a superior team, but with a couple of defenders and my GK out injured I was nervous. I also played with players that are usually on the bench (only two first team regulars) so their match fitness wasn't great. At half time I was down 0-2 and I had no real quality on the bench.. my defenders were losing the aerial battle and Sturm Graz was playing with a deep defensive line that made it difficult for my wingers to cut through. At half time I changed both my wingers from "attack" to "support" as well as changing one of my defensive midfielders from "defense" to "support" (they both had support now"). This meant that every player in my team played with "support" settings except for my striker as complete forward (attack) and centre backs (defense). This meant that 1. my team started to play more passes on the last third of the pitch, being a bit more patient with finding room to work with. 2. Instead of trying to run directly through a pack of defenders, my wingers now moved a bit more freely in front of the oppositions defence, varying their play in width and tempo, opening up room for themselves, and more importantly, each other! This meant my striker got played through on goal after full backs being lured out of position from patient wingers/playmaker, more players in dangerous areas for Sturm Graz to deal with, etc etc. I won the game 4-2. The goals came from very direct changes made at half time, and its always a joy to watch.
There are obviously many, many more situations that can occur, and if there are specific things you want any help with let me know. But hopefully this was helpful!
PS! english isnt my first language, neither in life or in Football Manager
, so please ask if anything is unclear