It is not allowed to add or remove entries to the OptionSetValues Property. It is allowed to change the text of an entry if the semantic is not changed, e.g. by fixing typos or improving the formulation.

If a specification intends to deprecate a bit, it can require that the validBit shall always be set to false. Adding entries is forbidden, because subtypes might have been defined using those bits already.

If a specification intends to extend the OptionSet, it needs to define subtypes with additional bits. Subtypes may also refine the semantic of existing entries (see OPC 10000-3). Note that the initial defined length cannot be changed in any subtype (see OPC 10000-3).