Manipulate the loading screen.
When you are at the loading screen, just tilt the analog stick in any direction. The little star thing will move around.

Open the Dressing Room
All you have to do to get to the Dressing Room is make sure you have at least 10 000 Meseta ON a character (NOT in the bank) when starting. A new option will appear, labelled, ''Dressing Room''.

Once in the dressing room, you can change your characters costume and hair-style, for the low low price of 10 000 Meseta (hence why you need 10 000 Meseta to open the option)

Unlock new difficulties
To unlock new difficulties offline: (They can be done in either Episode I or II)
Beat Normal mode to open Hard mode
Beat Hard mode to open Very Hard mode
Beat Very Hard mode to open Ultimate mode

To unlock new difficulties online:
Get to level 20 to open Hard Mode
Get to level 40 to open Very Hard Mode
Get to level 80 to open Ultimate Mode