I say this because the DV color space conversion to SDR or HDR10 feature is available in the nightlies and not in the MC bundled LAV filters, and that feature works for me so I assume it's using the nightlies I installed.
Except no such feature exists, therefor it also cannot work. I think you have misunderstood some upcoming changes or some details about the files you are playing.
All LAV does is export metadata, it does not, and will not, perform any conversions (they would be far too costly to do anywhere but in the video renderer). And MC also does not use the metadata (yet), so it would make no difference if its present.
If you don't specify a custom mode as explained above, MC will always use its built-in copy of LAV with no exceptions.
As for the custom mode, I would generally not recommend using it like that, because mismatches in versions can also lead to bugs. If you want to use it to change some settings in LAV, I would recommend using the same version as bundled with MC to avoid that issue.