1. After you put the clip in the bin, but BEFORE you put it on the timeline, right click on the clip and go to properties.
In the Videomode section under colorgroup, make sure it says it's XYZ. (if it's not, then change it)
2. Put the clip on the timeline and finalize out. (CTL F)
3. In the finalize pop up, click on the 3d lut button, add the XYZ to rec709 lut, then click ok.
4. Click on the check box next to the Video-3d lut. (or it won't actually apply the lut).
5. Set the rest of your finalize options and click render.
As long as you are starting with a XYZ clip, this should output it in RGB at the end.
*** This will apply the 3d Lut to the entire timeline. ***
Note: If you are opening an existing DCP, you must set the Jpeg2000 decode setting to DCI XYZ.
Configuration-->Defaults-->JPEG2000 Compression-->Decode JPEG2000 XYZ to--> DCI XYZ.
This will decode the jpeg2000 file to XYZ which will allow you to use your own 3D lut on the timeline.