Okay, here is my take o this particular situation.
The SRO was engaging the EDO in a contest of wills. He was wrong to do it, because he showed no justification for refusing an order, other than his own opinion. If he had offered a reason other than his opinion, he might have convinced the young officer to agree with him and change the order.
Here's the hook. What is "un-necessary" cool down to the SRO is a matter of opinion, as long as the additional cooling of the RCS does not cause the plant to violate the BFPL curve or some other procedural limit. If such a violation were the imminent result of opening the valve early, simply calling the EDO's attention to that fact would have been enough. The RadCon Manual prohibits "un-necessary" cooldown, because it results in un-necessary radioactive waste from the addition of makeup water to maintain PZR level which will have to be discharged on the subsequent heat up. If the added time with the valve open would have necessitated charging which would not have been needed otherwise, then this would have been a procedural violation. Again, this could have been pointed out to the EDO, who would most likely have agreed and rescinded the order.
There is nothing in this example which shows that either would have been the case or that the SRO was clear that one of the two would have been the case. All we have here is a situation where the SRO refused an order without justification. If he really had a reason to believe that opening the valve would result in a violation of any procedure, then allowing the EDO to open it would be dereliction of his duty.
In procedural matters, it is the duty of the SRO to advise and inform the EDO, whose decision is not subject to question at that point, and whose orders are to be obeyed.
In matters of judgment or opinion, the judgment of the officer takes precedence over the judgment of an enlisted watchstander.
So, either way, this SRO was wrong. He should be DQ and perhaps written up.