Yes, you can put breakout tabs in your library, and configure them as a mechanical components so they doesn't appear on your schematic or BOM. This is what I typically do. I typically place half-tabs on the board so that when the board is arrayed the half tabs on adjacent boards mate up, or where an embedded board meets the panel frame I just place another half tab in the panel file to join it. You could draw full tabs in your library and place them in the panel file, but then you lose the ability to set clearances on the PCB from your tabs. My tab outlines are drawn in two layers, one for the board outline with a closed-off end, and one for the overall outline of the panel with an open end. That way the board outline layer can still be used to set the board shape in the PCB editor, and once the board is dropped into a panel I draw the rest of the panel edges in the panel outline layer and have a finished routing outline.
Of course there are other ways to do it, just be sure that your tabs meet your fabricator's requirements.