From CloudModding MM Wiki

Codes that allow you to play around with the magic metre in Majora's Mask.

Codes by Volvagia356.

Change Magic Metre State (Normal, Double, etc.)
811EF6B0 ????
0000 - None
0100 - Normal
0101 - Double 

Infinite Magic Metre for:
801EF6A9 00??
00 - No Magic
30 - Normal (Fills up the magic to the size of the normal bar)
60 - Double (Fills up the magic to full
*You can also edit this for different Magic Metre amounts