Well, the 3rd token in the ini setting is the "Hide nicklist" setting (based on my testing just now), so if the INI really does have "#40_something=right,153,0,1" then it should already be disabled.
That said, I would probably try erasing the line completely so that mIRC will revert to default settings for that channel. I'd also look at other settings related to that channel in the INI and consider deleting those lines as well.
