You're right Shem, but when I saw that many files were exactly the same I wanted to try anyway.

Now, there's one mistery solved, I've found the cheat to drive the small ships:

Enter the following codes on the default player name option:
DROIDS = drive as rescue droid ships

Source: http://hem.passagen.se/odjobb/playstation/5582.html
And I've finally found which files contain the prototype tracks and I've replaced them by the normal ones. I changed the 5th prototype for Porto Tora and now there are doves in the track:

Code:
http://ultraboard.topcities.com/doves.jpg
This one is beautiful, it's raining in the first prototype track:

Code:
http://ultraboard.topcities.com/rain2.jpg
And here i am playing time trial in the prototype tracks:

Code:
http://ultraboard.topcities.com/ttrial1.jpg
http://ultraboard.topcities.com/ttrial2.jpg
Something strange happens when you replace the last two prototypes with normal tracks. You play the normal tracks with the special fastest ships, although they look like the normal ones. And when you play the prototypes, the ships are the special ones but with the abilities of the normal ones. So although they look like the regular ships, you can play any track with the special ships.