Currently registered devices can update FDI Device Package, DD, CFF, and H1 physical layer, and still maintain their current registration certificates.  

The DD/CF files can be updated by running a DD/CF test as described in the DD/CF registration process document, FF-531.

See: FF EDD/CFF Testing and Re-Registration

For FDI Device Package maintenance, see FDI Device Package Registration and Understanding FDI Package Versioning

ITK 5 registered devices can have their DD/CF registrations maintained via a DD/CF Self-Test using the last minor version of ITK 5 (5.2.0).  

See: FF EDD/CFF Testing and Re-Registration

Changes are not allowed to the stack or function block application; these changes require a new device revision and a full ITK test on the latest version of the ITK.  Details can be found in the Device Registration Process, FF-524, or FCG PD10026.

See: What are the requirements to register an H1 device?