How to modify a rig after adding motion to a control rig

I have a question about control rigs.
I created a rig, added motion in the sequencer, then added a new control to the rig for adjustment, but I could not key the new control.
The motion itself is not broken and when I select the Rig I see the new controls added.
If I want to edit a rig after motion has been added, is there some special procedure I need to follow?