83E1000C is the original load instruction to r31, at offset 0xC from (r1). 60000000 is a nop, meaning no operation. This causes r31 to never have the new value loaded into it. This is very likely not a "real" speed modifier, but rather something that causes the game to lag, although I haven't ever used this code myself so I can't say for sure
Super Mario Eclipse, what Super Mario Sunshine could've been.