You're right. I gave it a test with the combo number timer never decreasing and I guess I never played long enough to get that 150 limit that it doesn't mention, so that makes the timer toggle code not as useful. I found a code to prevent that kill counter from increasing making mercenaries endless until time runs out or you die, and another line to change the limit for BLUS30491:
Mercenaries Mode Stage-Ending Kill Counter Never Increases
0
bungholio
0 00022EFC 396B0000
SET OGP=816A0300396B0001916A030081390000 SET COP=816A0300396B0000916A030081390000
Mercenaries Mode Limit Modifier For Enemies Killed Needed To End The Stage
0
bungholio
0 000136C0 2F80Z
[Z]0095=Default 150 Enemies;0001=The first kill wins;0009=10 Enemies;0063=100 Enemies;00C7=200 Enemies;01F3=500 Enemies;03E7=1,000 Enemies;270F=10,000 Enemies[/Z]
SET OGP=800900582F800002409E0200800903002F800095419D0108 SET COP=800900582F800002409E0200800903002F80????419D0108