I doubt that any organ builder was involved. After all, the organ is owned by the church, not the organ builder. Sadly, it's common practice for speakers for an electronic organ to be hidden behind organ pipes. I personally think this is downright dishonest - aside from the all too frequent destruction and damage left behind by unsympathetic "installers". Being cynical, I wonder if it's a ploy to make it more difficult & costly for the church to return to pipes when the electronic dies - in the hopes of getting another sale?
As far as I known, in Catholic churches, the parish priest is the one who makes this sort of decision - which is why back in the 1970's, at least one electronic organ distributor was targeting RC churches as easier to sell to than most other denominations, because you only had to convince one person.
As to Historic Organ Certs. - they have no legal standing - but issuing a certificate does sometimes make the church concerned realise what they've got, and just maybe try and preserve it. A typical situation is the Holt (pipe) organ in the former Primrose Hill Baptist church in Huddersfield, that I mentioned in an earlier post. No-one in the church, or on the Yorkshire Baptist Associations property group knew what they had - it was just another pipe organ. It took me 1 e-mail to establish who the builder was - but at that point, exchange iof contracts with the developer was only about a week away. If the organ had been recognised earlier, then maybe a HOC would have meant that earlier efforts to rehouse it could have been made (one can always hope!). In that case, the stop list alone indicated a fairly old instrument - and as it happens, it's an even rarer survival than the organ at Wealdstone.