Ok, I see that perhaps a member overlooked the actual inquiry. Not can one import a Nikon Custom Profile into LrC (answer to that is no, and I think only XMP profiles, DCP profiles, and LCP lens profiles are supported, see REF 1) but how to save/convert a Nikon Custom Profile to a format that LrC can use.
Now, I am not a Nikon user, so I had to Google on this. If I have this correct, a custom Nikon Profile is created by the user using a Nikon application (Nikon Picture Control Editor, REF 2, or perhaps the Nikon Picture Control Utility 2) then saved to the camera (or can you do all of that in camera??)
And the format for the file that is created/used is. ncp (a file format LrC has no capability of using)
My first kneejerk thought (as in wrong) would be to look for a source that has profiles for Nikon Cameras for use in LrC. But NO, that would not be for custom profiles the user created, but for standard ones Nikon created (that are basically emulated via camera matching profiles, and not what you are looking for) or ones the author created for their work (that will probably not be you inspirations)
So, in this case, some sort of software or update to software that can save the profile into the required format.
No answer just yet.
P.S. I assume you are frustrated, please take a breath, Replying tersely to a members reply is not wanted or appreciated.
REF 1) https://www.lightroomqueen.com/classic-import-profiles-presets/
REF 2) https://nikonpc.com/