Yes you can.. I figured it out the issue I was having. When you are creating a mygm, the last option says "use custom roster" yes or no... When you change it to yes and advance, your own roster is at the very bottom of the list.. Scroll down, even though it says a different gamertag, it is infact your created roster.. I loaded it up and it worked flawlessly..
The issue of putting Irving on the Bulls to trade for picks, is Cleveland's salary cap. You'll need to put someone else on their team from Chicago like Muhammad in order to make the dollars work, at least that's what I had to do