Here it is..I know the DMA code is weird...but it works..Turn on while editing room and press D-PAD Right to modify players to 18. Start the game and evry could see "'#'/20 Max. Players". LEAVE IT ON

#20 Player Room[Hz-15]
;Noss
;Turn on while editing room
;modify the players to 18
;UNRANKED GAMES ONLY
0xFFFFFFFF 0x006BE87C
0x0002565C 0x00000014