The default schema as distributed with the UnboundID Data Store (currently schema files beginning 00- through 20-) is not intended to be modified in any way. It follows current standards, and in many cases is required to match the actual implementation of various features and changing it may cause problems.
However, from time to time it may be necessary to change the default schema definitions.
Usually, this is in relation to the writability of various operational attributes to allow them to be modified. It needs to be pointed out that in virtually every case these are read-only because that is the way the standards define them, but in some cases there are inter-dependencies between various attributes and even with the code of the server itself.
Modifying these should not be undertaken lightly, and if possible only after a discussion with UnboundID Support who will help evaluate the risk. Any such modifications should be temporary, and should be restored as soon as possible.
The best practice in these cases is not to edit the schema as distributed, but to take a copy of the schema entries in a file loaded late in the schema loading process (e.g. 99-overrides.ldif), and place the modified version there.
Later definitions of existing schema override earlier definitions. A warning is generated as the overriding schema is loaded (a useful reminder that the non-standard override is active).
To restore the original schema, simply remove the overriding definition (or delete the file containing that definition).