Go to the training garage in the City Park. Select the pro skater you would like to play as in career mode then select any of the tutorials on their list. Once the tutorial starts, skate over to the two big garage doors that are on one side of the training room. One of the doors has a big arrow on the ground that is pointing towards it, and the other door has a big arrow on the ground that's pointing away from it. Stand on the arrow that's pointing towards one of the doors, and it should give you the option to leave. Use that to leave the training building, and you will appear in the City Park again as the pro skater.

Your tricks will not change to the pro skaters trick set, like they do in Free Skate mode. The tricks will remain the same as you had them set. Also, you will not be able to change anything on any of the pro skaters in your room (clothes, eye color, hair color, etc.).

The only way to change back to your other character is if you go to your room in Suburbia and recreate your skater. Before you can recreate your skater in your room, you will need to select one of the default looks so you aren't a pro skater any more (since you can't change anything on the pro skaters). Quitting the game without saving will not change you back into your other skater. If you do that you will still be the pro skater when you return to the game.

If you use this glitch, your hospital bill and broken bones will not appear on the screen like they normally do, even after you change back into your other skater. To fix this, go back to the training garage and select the same pro skater as you chose the last time that you left the garage as a pro skater. So, for example, if I changed into Lyn-Z, exited the garage, then went back and changed into Tony Hawk and left the garage, I would choose Tony Hawk this time. Once you’ve selected the character you used, start any tutorial (it doesn’t need to be the same tutorial as the first time). When the tutorial starts, pause the game and select ‘go back to [skater’s trick type] menu’, then ‘Go back to Training menu’, then ‘Exit Training’. If you never went to your room and changed back, then you will till be the pro skater. If you did change back, then you will be the skater you made. Either way your hospital bill and broken bones will work now