Hi beginner.....
It just sounds like your penis is becoming more vascular what with the extra work it is now doing. So as more blood is being moved around in it the veins need to be bigger to accomodate this. The fact that they move around is of no significance - mine do this also this is because they are just under the skin and not attached to anything.
I wouldn’t think this would be dangerous - just watch out if the veins become firmer or even hard and painful - erect or flaccid. This is an indication of a thrombosed vein, but take it easy and this should not happen.
I speak from experience on this one as i am going to restart pe on sunday after an enforced couple of weeks off waiting for a thrombosed vein to heal. Very frustrating.
Have a read of the thread entitled “hard vein…” (in the main members section) to see if it sounds similar - although it doesn’t sound like you have a thrombosis.