You must add a feature that let make changes to the teams management line ups before starting the game. like other sports video games do. In the current game that option is available when the game already started, and you end up with no other option the spend one substitution, if you wanted to make any alteration to the initial roster. here is an example on the rugby 20 video game.

Hi ,
I think the only way you can get around this issue at this time is to make team changes in the edit team section.
For Example if playing with a Super Rugby team , go to Super Rugby Team listings and choose your team to edit with the line up before starting a single match. I used to do this in RC3. But your suggestion is good if they can build this into the game in the future.
I agree there needs to be an edit starting lineup feature before a game begins and giving you access to your entire squad not just starting 23.