As for zooming to the Center of the screen while routing there really is no command for it. But for the Xpedition flow we work a little differently.
While routing, as you get to the edge of the screen, you can hold and drag the Middle Mouse button to pan wherever you like. If you are using the Plow Style Dynamic, and Auto pan is enabled in the Display Control, your screen will auto pan as you reach the edges.
As for Vias, this was answered above, but it should be noted that while interactively routing, you can RMB and change your via selections for placement of new vias.
Thanks for the responses. The padstack processor seems more geared towards larger updates. And I get about setting the via prior to placement. I was just looking to see if there was something like an RMB pulldown (less mouse clicks) that would let one swap individual via, but it seems that going into it's properties or the padstack processor are about the only options.