ISO 15926 Part 5 has been superseded by an annex to ISO TC184/SC4 : Procedure for development and maintenance of reference data in database format
What does that mean ?
Part 5 described the method to maintain Part 4 in a database format. As the standard was aligned with another standard it has been replaced and is not longer a part of ISO 15926.
The procedure defines how a database can be submitted and approved by ISO member countries.
There is a formal process for extending the ISO components in the reference data, which the following web site exposes.