[Closed] Visio 2013 Shapes

Anyone know how to edit a custom stencil in visio 2013 that I've copied from a built-in one? I've got a round table stencil & all I want to do is ungroup the bleeding thing so I can chop & change the number of chairs. But no, that would appear to be beyond the capabilities of visio which appears to have morphed from being a simple cad-u-like into some sort of inventory management bloatware riddled with functionality that nobody really asked for.

If I see the "[i]Shape protection, container, and/or layer properties prevent complete execution of this command[/i]" dialogue one more time I might just lobotomise myself on this pencil.