The process works by defining DICOM tag names for these private tags. These values are passed into the CLI command in the form of a CSV file. Once tag names are defined for the Private tags, then the DICOM tag names can be used in the custom profiles just like any standard DICOM tag.
The command line optional flag for setting these private tag names is
Where private tags CSV file is formatted as:
Tag,VR,Keyword,Description,VM 0x111021b0,UN,UnknownProperty1,An unknown property,1
In this case, the Tag is the (1110,21b0), the Value Representation (VR) is UN, the Keyword (or DICOM name) is UnknownProperty1, the Description is `An unknown property`, and the Value Multipicity is 1. NiBabel has a good explanar on what these values mean.