I'm working on a tool that establishes data connections using ADO, as well as whatever connections are automatically established when ArcObjects query commands are used. The default connection settings ("AUTHENTICATION_MODE", "SERVER", "DATABASE", etc.) can be read from a .SDE file and stored in an IPropertySet, and if the user modifies those connection settings, they can be saved to a new .SDE file. That all works fine.
For the extra settings needed by the ADO data connections, I can store them in custom properties in the IPropertySet, using property names like "CUSTOMTOOLNAME_PROPERTYNAME", but when I save the IPropertySet to a .SDE file using an SDEWorkspaceFactory, all the custom properties get stripped out prior to saving. Is there any way to store custom properties in a .SDE file? Even a difficult method is acceptable, if there is no easy method.