Just want to confirm something; when you look on a player card, you can see position ratings, ie for a QB on my roster, ratings are there for QB and RB.

I'm correct in thinking that the ratings displayed are there for positions that player can be converted to, so if I select "Change Pos", he can only be a QB or a RB.

He can however be put into the depth chart as say a FB - but cannot be changed to a FB - and will receive a rating for ability to play that position, but receives an out of position penalty.

Is my understand correct and does this apply in all leagues?

Everything sounds right to me except the out of position penalty. It's possible but I'm not sure any penalty is used beyond the fact that the player lacks the primary skills as a FB which are run & pass blocking with RB skills being secondary.

You can override a QB with RB skills for formations that have the FB as the ball carrier without penalty. He may represent as a 27/47 rating in the override screen as a FB but if he is put into a position where he will run the ball then there isn't a out of position penalty since speed, ball carry, avoid fumble and break tackle matter and not his blocking skills

It's just like using a 95 speed DB in an override at LB in a formation where say the WLB blitzed. Only speed, acceleration and pass rush skills matter in that case so run defense and M2M skills aren't used.