Okay, so the question is, do I hold out for the 2 pack instead of getting Runamuck on his own?

If I get him seperate and if the 2 pack is released as the "only way" to get Runabout, I'd have spent that money for a duplicate toy.

Another question is it a true repaint or do they just swap the white plastic for black?
It looks like they use a single solid color instead of just painting the plastic.

Yes, I imagine they'll have to repaint some details, the paint layers that worked on white might not necessarily be compatible with black.
Also, from memory, Runabout had a red/orange eyeslot while Runamuck had a blue one.