Assuming you have kept a reference to the rollbar object:

var rb = DynarchRB.setup(...);

you can later access a few properties.  Not sure if the "tabs" property is documented, but anyway, it keeps an array with references to each tab element.  You should be able to hide a tab like this:

rb.tabs[1].style.display = "hidden";

and later make it visible with:

rb.tabs[1].style.display = "";

Note that the above will hide/show the second tab.  As in any JavaScript array, indexes are zero-based—to hide/show the first tab you'd use rb.tabs[0].

Hope this helps.