I have my own guesses as to whether this was wise, but does it even sound feasible to you Test Pilots out there ?
I guess it depends on which alpha limit he went to - the AFM limit or the Flight Test Envelope limit. I don't know whether the Trident stall was pusher defined or not, some T-tails need a pusher defined stall (Challenger, CRJ), some don't (Learjet 40/45).
If the Trident was pusher defined and he went beyond pusher alpha by disabling the pusher - then definitely not the smartest trick in the book without an accurate gauge or FTI. The risk of deep stall being all too real at that point. If like the LJ the stall is defined as "two seconds on the aft stop", then going to within one degree would be less of a risk although still not smart without a very good reason to go there.
FlightTEster