1. Add duplicate track without effects to multitrack.
2. Then apply effects to original track in single track mode and then add it to the same multitrack project.
3. In multitrack mode original track with effects set the volume envelopes to "0" during the part you don't want the effect.
4. Set the volume envelopes opposite in the duplicated track.
Additionally you can adjust each track individually in the Waveform editor by double clicking on it.