Extracting and remuxing HDR metadata without reencoding video?

So, there are two encodes from the same source - one without the HDR metadata and one that's with. I was hoping MKVToolNix may have a function which allows you to do what I'm requiring about, but perhaps it's not that simple (should be possible I imagine, though I'm not sure how linked the data is to the specific x265 parameters, or whatever other codec, set for the encode). Is it not just a header file which goes by the effective time/framerate of the video stream (irrespective of compression methodology)?

In any case, if somebody knows of the effective tools/software and accompanying steps (whichever aren't obvious) and can provide them here, that would be very much appreciated. Thanks in advance!