the modifiers only work when choose CUSTOM difficulty for batting/bowling (instead of the easy, medium, hard, hardest).... pro/legend etc are for AI difficulty... the only modifiers that will work for AI are the PHYSICS modifiers.
There's no custom option for the player to select.
It was in dbc17 but not in ashes.
In ashes u have to select ur batting/bowling difficulty level and then change the values of that particular difficulty level in batting/bowling modifier section.
If u say select easy as the difficulty and change the modifier for say hard level , then u won't get the desired results.
Over-all the implementation of the modifiers are a little tricky for a new user.