ok. I've figured out you can slide players in formations.
No idea how to save - it so far has always said failure to save.
No idea how to bring in a player to a formation that is not already listed in the formation.
Really, no idea about any of this at all other than it can really make a difference, and it took me quite a while to figure out that you had to "slide" players...
Can someone please explain how this works?
Muchisimos gracias!

Nm, figured it while combing forums. Not in game planning is this done, but in the overrides tab in depth chart for any on else who is curious.