As a side note, I changed the IFs to Wingers on mine, which led to success on mine, but that could be due to the players I have. Lincoln has been awesome for me as the winger there (and only one who can take a reasonable free kick!) but his right foot is pretty damn dodgy, so have refrained from using him as IF.
I found that the IFs struggled to get shots in because the middle of the pitch was so full. Time and time Mahrez would cut in, get in a great position but the shot would be blocked by one of the F9s!
By using wingers, they are more likely to get a cross in and with 3 strikers in the box, there was also a fair chance someone could get on the end of it.
I'm still on FM2016, and just started a new safe with DSD with Sporting Lisbon only one transfer. It is a tough team to start with, not the best transfer budget and the defense is quite bad. Now my start has been good. The question is when you say that some player roles can be changed which ones are you referring to, since I've notice that F9's can't be changed or it will affect the tactic attacking performance.
Yet again test division, this time with Crystal Palace. Added a lot of players in the CA range of 135-139 to create more options and also made some additionional positions for several players as natural to really have the squad depth. Since the best players at the club are above the 140 CA , it did not changed the media prediction, it is still 12th.