http://users.boardnation.com/~jamstubbs/index.php?board=25;action=display;threadid=750

Player Control/Type
credit: kryogenics

Turn into a referee, human, etc. mid-match

D1064880 2000 press z on controller 1
8015AF99 00xx player 1 = xx

D1064880 2200 press z + left on controller 1
8015B2F1 00xx player 2 = xx

D1064880 2100 press z + right on controller 1
8015B649 00xx player 3 = xx

D1064880 2400 press z + down on controller 1
8015B9A1 00xx player 4 = xx

{Game does it}
[Hacked and observed]

 _______ Unused?
| ______ Team
|| _____ Legal Man?
||| ____ ??
|||| ___ Referee
||||| __ Interference?
|||||| _ Ringside?
|||||||
|||||||
0000001 = 0x01   Ringside Human
0000010 = 0x02   [Interfering Human]
0000100 = 0x04   {Referee Human}
0000101 = 0x05   Referee Computer
0001000 = 0x08   {Computer - Tag Match | 1P (CP) vs. 2P CP}
0001001 = 0x09   {Ringside Computer}
0001010 = 0x0A   {Interfering Computer}
0001100 = 0x0C   Tag Partner Computer?
0010000 = 0x10   {Human - All}
0010010 = 0x12   ? Human
0011000 = 0x18   {Computer - All}
0101000 = 0x28   {Computer - Tag Match | 1P CP vs. 2P (CP)}
0110000 = 0x30   {Human - Tag Match | 1P CP vs. (2P) CP}
0111000 = 0x38   {Computer - Handicap Match | 1P 2P vs. (CP)}
|||||||
|||||||__ 1
||||||___ 2
|||||____ 4
||||_____ 8
|||______ 16
||_______ 32
|________ 64

IDA says the code is around loc_8017E808 in the ROM, so check the db for it.