Writeable configuration values

[mkarg]

In case an application wants to provide an integrated feature (e. g. "edit" button in the GUI) to edit configuration values, it would be great to have support for writeable configuration values (possibly in a future version of this API).

[struberg]

I think this is not a core functionality of the ConfigJSR itself.

It is perfectly possible to register a custon ConfigSource which can do that for you.
We even built such a thing for the TCK of the ConfigJSR. Feel free to just pull it over to your project. It's ALv2 licensed, so no issue.
https://github.com/eclipse/ConfigJSR/blob/master/tck/src/main/java/org/eclipse/configjsr/configsources/ConfigurableConfigSource.java