I agree we should be able to have 2-3 different saved army compositions. My Multiplayer is indeed different than my War army.
As far as the free retrain we still only have (1) per day but you can only retrain the army that you just lost. Eg. if you just lost your mercs, HT, and planes in War you can now retrain that army. But if you had a MP army already training that would still be unaffected.
Being a casual player myself, I just want to have my army ready to go when I log into the game. I hate having to worry about redoing my tactics and entire army just so I can war. I've actually opted out of the past 6 wars because I've gotten fed up with trying to switch and waste time retraining my army. I have struggled to keep my coalitions filled because of the constant need to switch army compositions.
As a side note I'd also be more inclined to use mercs and generals in MP battles for added fun because I could keep my War army fully loaded and ready to go without consequence. Further, I'd have lots more fun with a third army so I could try different compositions in multiplayer or just keep it fresh. One battle being all out HT or in the next moment using commandos.
If you could select the army you want within the first 30 seconds before a battle regardless of war or not that would be cool. It would be a lot more attacking strategy and give you the ability to adapt on the fly to the type of base you are presented with.