I would leave it alone and repot after blooming is done.

Thanks I really was thinking just to leave it in that container. It is a light feeder I suppose so I will not really fertilize it and when I do at a low strength.

I am really tempted to replant it in a little bigger pot in some 5-1-1. I would need to get all the soil off the roots, should I run them under water to wash all the soil off. Should I really wait till it is done flowering?

Rhododendrons are not heavy feeders - yellowing leaves are more often a sign of needing iron or magnesium, not nitrogen. It can also be an indication of overwatering, or watering with alkaline water.

The most damaging time to move or replant is during the period of active growth....that period that immediately follows blooming. Rather than wash/remove all potting medium, you can root prune - cut 1/2" to 1" from sides and bottom of the rootball, replant.