ISO has appointed the Unicode Consortium as the Registration Authority for International Standard 15924, Codes for the representation of names of scripts. Changes to the set of registered codes must be constrained by the requirements of backward compatibility.
The registration authority may add codes or make certain changes in codes that were previously assigned in the registry. To minimize the impact on existing implementations, however, there are limitations imposed by the registration authority on the types of changes that can be made by the registrar.
This document lists the policies of the Unicode Consortium regarding registered code stability.
Assignment. Once a code is assigned, it will not be reallocated, removed, or reassigned.
As a result, implementers can be assured that the registry of ISO 15924 Script Codes is strictly cumulative. The registry may deprecate an assigned code (that is, formally discourage its use), but it will not reallocate, remove or reassign the code.
Four-letter Code and Number. Once a code is assigned a particular four-letter mnemonic code and a number, these will not be changed.
The numbers and four-letter codes are used to distinguish between registered items. They are designed to be used programmatically, and thus must be stable.
In some cases the English or French names chosen to represent the code may be inaccurate in one way or another. Any such inaccuracies may be dealt with by annotated changes or by adding descriptive text to the registry.
Note: It is possible to produce translated names for the entries in the registry, to make the information conveyed by the name accessible to non-English and non-French speakers.