Here's an audio chain allowing you to transform a stereo signal from left-right format to mid-side format, process the mid and side components separately, then transform it back to left-right format. Use the "M Process" and "S Process" Graphic EQ devices to EQ and level the mid and side components separately. The audio chain is based on the following maths:
Mid = Left+Right
Side = Left-Right
Left = Mid+Side
Right = Mid-Side
Here's how the audio chain works:
• The original stereo pair coming from the AudioTrack device is split into two copies.
• Two Panorama devices calculate mid and side mono signals from the left-right stereo signals.
• Two Graphic EQ devices apply processing to mid and side signals separately.
• The processed mid and side signals are split once more and a Panorama device reverses the side signal.
• Two mergers calculate the left and right signals respectively.
• A Minimixer device combines the left and right signals into a stereo pair.
Note: You might use this setup for example as part of your mastering chain. Depending on your processing, the end result might clip. I recommend adding a Gravity compressor set as a limiter at the end of the chain to avoid it.