I'm always cautious about these things amd so to be on teh safe side, I'd rather not eat these things unless it's promoted as edible.

I know as a child we grew the real sweet potatos (not the ornamental kind) and we would steam the leaves and use it for salads. The colours of those leaves were dark green and sometimes purple. They looked very different from the ones I've seen here. I don't really know much about the hybridized potato and perhaps to be on the safe side, contact the source of these plants to see if it's true.

As for pinch growing tips of the vine.. The answer is yes. I do it often. In fact, many tropical plants are started through cuttings.