How to add Spatial Reference ID 28992 to MSSQL server?
I want to use Spatial Reference ID 28992, as found on EPSG, in MS SQL Server. How can I add this to MS SQL Server?


As you've mentioned, there are ways to modify system catalogs manually but in general this is not supported or recommended. As such, I consider this a non-option.

The documentation specifies:


  SQL Server supports SRIDs based on the EPSG standards. A SQL Server-supported SRID for geography instances must be used when performing calculations or using methods with geography spatial data. The SRID must match one of the SRIDs displayed in the sys.spatial_reference_systems catalog view.


Emphasis mine. 

So it seems to be clear that SQL Server does not support this particular SRID (as of SQL Server 2019 - db&lt;>fiddle).



That being said, you should 


Create a feedback item for the MSSQL team about adding this functionality. 
Look into PostGIS which is widely considered the best option for handling GIS data in a relational database (and free, to boot).