It should be possible to define custom commands in a TreeDefintion file, extending the functionality further than the statically defined built-in ones.
I've made a change to the C1 Core here which adds this ability, where commands can be defined as classes and elements added in a TreeDefinition file through a custom namespace.
https://bitbucket.org/actoas/composite-c1-acto-build/commits/915820dd0b58f30e275569b6f3ea87d82e169aa6
In this commit there is an example of such a custom command https://bitbucket.org/actoas/composite-c1-acto-build/src/915820dd0b58f30e275569b6f3ea87d82e169aa6/CompositeC1/Composite/C1Console/Trees/SortDataTreeActionProvider.cs which can then be used in a TreeDefinition file.
I've made a change to the C1 Core here which adds this ability, where commands can be defined as classes and elements added in a TreeDefinition file through a custom namespace.
https://bitbucket.org/actoas/composite-c1-acto-build/commits/915820dd0b58f30e275569b6f3ea87d82e169aa6
In this commit there is an example of such a custom command https://bitbucket.org/actoas/composite-c1-acto-build/src/915820dd0b58f30e275569b6f3ea87d82e169aa6/CompositeC1/Composite/C1Console/Trees/SortDataTreeActionProvider.cs which can then be used in a TreeDefinition file.