IEC 62386-105:2020 applies to control gear and control devices.
Typically, a bus unit according to IEC 62386 (all parts) contains firmware. There are circumstances where it might be necessary to change the firmware after production or shipping of the product. For example if the bus unit does not operate as intended. In such a case, a firmware update of a bus unit via the interface is beneficial.
This firmware update process is primarily designed to be a bug fix process, not a feature extension process. Nevertheless the firmware update process can be used for feature extensions. But it is important that the risk of negative effects to the complete system is considered in detail.