From LightSpace export A Null LUT Image, and a LUT Image combined with the calibration LUT data using the 'Add LUT' function ('Edit / LUT Manipulation / Addition'), or by using existing profile data to build the LUT on-top of the Null LUT Image, as explained above.
Export the Null LUT Image and Calibration LUT Image as DPX or TIF images, and load into Photoshop, with the Null LUT Image as the lower layer, and the Calibration LUT Image as the top layer. The background layer is a bright block colour to show where the 'reveal' is being applied
Using the graphics program tools - 'Select Colour Range' in this case - isolate the areas of the top LUT Image to be replaced with content from the lower LUT Image.
The effect of the selection can be seen using the block colour background by momentarily disabling the lower LUT Image layer, as shown below.
Re-enable the lower LUT Image layer, and save the combined image as a new TIF image file. Import this modified TIF image into LightSpace, where new LUT data will automatically be generated.
The following image shows the new modified LUT data, and when you hover over it the original un-modified LUT data, showing the alteration to the higher-end of the grey scale.
You can easily see the change in the highlights between the before/after LUT graphs.
The new LUT data can then be exported for use in any external LUT box or DI system