Does this describe what you're attempting...
Select a clip.
Open the audio room.
Move the scrubber (red line) to where audio level is to change.
Move the slider/s of the respective channels to the desired levels.
When you do that you should see the white horizontal audio line on the timeline clip move accordingly, as a new keyframe is created at the scrubber location.
Exit the audio room and play the clip. The white line should not change, and your adjustments should be preserved.