I see the only way to do this now is changing the jersey file itself with another. In previous games I made a backup of originally home and away jersey then copied some interesting retro\alternate jerseys in any folder and renamed them to uhxxx.iff\uaxxx.iff (names of original home\away jerseys) and then just copy them to the main folder replacing standart with retro but in slot for standart.
in this year we can create f.e. folders 'home standart' and 'away standart' and export there home\away standart jersey's .iffs (let they be unknown_111111 and unknown_222222) accordingly using gregkwaste's 2K15 Explorer then export all desired alternate\retro jerseys using the same algorithm and then before every game import chosen alternate jersey to unknown_111111 for home or unknown_222222 for away games.
the only problem in this method (except that U should do this by yourself before almost every game) is accessories colors 'cuz the game thinks that U are using standart jersey and uses standart jersey's colors for accs.
uh and another problem is that in this year letters and numbers for every jersey are located in the separate archives so we need to copy 2 archives for every jersey (or 3 if we need correct preview also). but maybe in the next releases greg will add some kind of command-line function then it will make this method much easier.
P.S.: sorry for my English I'm almost sleeping
