What will happen?

When I trade players through dbf?
Any way for a 100% sure trade?
Thanks in advance.

Not really. Once I tried to sign a player through dbf and the rosters reseted to default.

its really not that difficult, as long as you know what you are doing

If you muck around you can make them free agents and sign them. Make sure you have a back up of your Dynasty to test it on. You can change players from team to team, just not directly to you team. Change their team number to suit who you want them to play for, make sure the roster positions get swapped as well ie player A team no. 3 roster pos. 13 swaps with player B team no. 29 roster pos. 6 each needs the others details to swap correctly.

I can't remember exactly, but, to get a player to be a free agent make their team to be 50 (change both the team listings ie orig team and payment? team)and change their contract details so the have no years left in the contract, you can even set how long they will want to sign for and how much. If I'm not clear enough have a look at a players details you know is on free agency and copy those details. Just have a muck around and you'll get it, and it can be fun once you work it out you can sign anyone.