I think Griff is refeering to your first thread idling for a "minute or maybe two" and yes after engine is already up to operating temp a minute or two is long enough to potentially be a hazard. If its condensation I highly doubt it would puddle in ports nor would cutting off water supply to exhaust do any good. If you do decide to pursue I would only use manual ball valves. What cam are you running?

I bought a 12v shut off valve . I was going to actuate it while idling to prevent water thru the intercooler at idle but then never ended up using it.

I've got them,one electric valve on each motor connected to the water rails on the 525's.
I only use them with a momentary switch to stop water sitting in the manifolds when the boat sits.

Your EGT at idle is going to be in the 600 degree range. You should NEVER shut off water flow to the exhaust manifold itself. If you just absolutely HAVE TO try this, then use ported plates at the riser junction like the Gil manifolds use. That way, you can dump water AFTER the manifold, but before the tailpipe. The water-jacketed manifold will act as a heat sink to pull the idle gases down under 300 degrees by the time it hits the elbow.