One method that is very easy is to Split that section out of the clip. Place the cursor at the beginning of the section you want to apply the effect to and press S to split. Add another split at the end of that section. You'll now have three pieces on the timeline and you can do something different to each one of them.

Better yet is to use keyframes. In the effect dialog box there is a small timeline at the bottom of the window. You can add points to that timeline and set different parameters for the effect at each point. The effect will gradually change from one set of parameters to the next as the clip plays back. You can change the points to "Hold" to have the effect instantly snap from one setting to the next instead of gradually changing.