You don’t necessarily need to interfere with the manager, just make sure he is doing his job properly by making sure when he wants to sign a player he has completed the research adequately? In other words KTs job is to make sure the manager is doing his job.
I do take the point but I'm just playing devils advocate slightly. Let's take the example of Berto. Let's say Kelvin asked Jimmy for all he due diligence on him and Jimmy duly delivered a report to the chairman. Obviously there are a lot of possibilities at this point but let's pretend there are two scenarios;
1) Jimmy knows Berto has a questionable temperament but really believes he could be the spark that saves his job, so he "enhances" the report a little. Kelvin checks and see's nothing to concern him so sanctions the signing. He's done what you suggest and we've signed him.
2) Kelvin gets an independent report on Berto, see's the red flags (cards) and refuses Jimmy permission to sign him. We get relegated, Jimmy gets sacked. Jimmy leaks it to his friends in the press that he had lined up Berto's signing but was vetoed by the club. It is picked up on here, Berto is researched, get's a glowing reference from Forest fans. We've gone down in a defensive whimper and we see this cult hero, creative winger that our manager wanted but our chairman wouldn't let him.
In scenario 1, we are where we are today and the Chairman is blamed for not making sure the manager is doing his job. Scenario 2, the chairman is blamed for not backing the manager.
I know I am reaching a little bit here but I'm sure you can see how both ways of working would be spun on here.
Maybe a Director of Football is the way to go, but then who decides the signings? If we repeated this season would we sack the DoF and keep the manager? Melville (rightly) gets a lot of stick on here but how many of our signings were decided by him or is he just out scouting the managers targets & making recommendations to the manager?