Is there a way to make a blank measure

Not in Chords-Only mode, but it works in the arrange window: simply blank out the portions of a phrase's Figure. If the phrase is not stored in the container, you need to make a snapshot of the Figure first, in order to be able to edit it.

In Synfire, I would insert a new container that has the Pause parameter set for the desired instruments, however. This way you can move the "pause" around freely and even change its duration by resizing the container.