Question regarding multiple versions of the same character.

Can someone provide feedback or an explanation of the following. Let's use Goten as an example and perhaps it applies to others as well.

In the game you can select multiple versions of Goten. There is Goten, Goten Super Saiyan, Gotenks, Gotenks Super Saiyan and Gotenks Super Saiyan 3.

Lets suppose we select Goten. During a battle can we transform all the way to Goten Super Saiyan and then all the way to Gotenks Super Saiyan 3 (provided we can fuse I guess we would have to select Trunks too).

In other words if you select Goten you can only play as Goten and are limited to his programmed moves or can we go from base Goten all the way to Goten Super Saiyan 3 during a battle and get access to new moves? Or the only way to play those characters is to select them from the start?