I just need to know if the mod allows you to do the opposite...

I mean reducing the range instead of increasing in the config.?

Because in the description it only talks about how the increases range of detection....

Currently only through individual overrides. minHostileFollowRange sets the minimum follow range of hostile mobs (as the name implies) but mobFollowRangeOverrides actually overrides the follow range of the mob regardless of whether the original value was higher or lower.