Harry,
haven't worked with footage from the Technicolor CineStyle, but have worked with RED and Epic R3D.
Don't think there's anything to fear with the LUT issue. Generally, the LUT is applied when transcoding from a RAW format into
your FCP friendly editing format. You can have many different types of LUTs installed without affecting your global FCP settings.
Typically when editing with FCP we are already working with a linear video file that has a built in LUT, most commonly REC 709.
It sounds like you can install a plugin utility called LUT Buddy that allows you to apply different LUTs to different footage right in the FCP environment, so you
would use the S curved LUT for just the CineStyle clips.
However, I would experiment with transcoding your CineStyle clips with S curve LUT separately, making them into ProRes with the S LUT "baked in" on transcode,
then you have the S LUT on those clips only, and you don't need to mess around with applying different LUTs in your FCP editing environment.