Possible? Yes! But not recommended.
There is nothing technical that would stop you from doing it. Thrust Reversers can be selected any time on the ground and there is enough thrust available to move the aircraft backwards. It is also not technically prohibited to do so:
Intentional selection of reverse thrust in flight is prohibited.
Did Dassault have some magic trick up their britches
It was an era of innovations. Have you seen the Vickers VC10 thrust reversers? The clamshell / target doors can be made internal within the nacelle. Literature is lacking on the Mercure, but there is a nice hint from a cutaway drawing:
Source: Air Enthusiast magazine, via aviadejavu.ru
The highlighted ...
Yes. Most of the noise you hear from aircraft is not mechanical noise from engines but disturbances in airflow around the airframe and engine outlets and inlets.
The airflow from reversing jet engine is much more turbulent than when the engine is forward pushing and thus more noisy.
"Possible" as in, "last flight out of Saigon, we'll try anything because the alternative is worse," maybe. But Boeing doesn't publish any procedure for it, as far as I've ever seen, and they generally take a very dim view of using T/R's at low speed. It isn't in any published non-normal procedures.
I've also heard, anecdotally, of one ...
Smaller airplanes with both rear-mounted and under the wing engines used to have "bucket" type reversers, which captured both hot and hold exhaust. However, a bucket is not a tenable solution for large diameter engines. Fortunately, in modern turbofans the cold thrust is the vast majority of the trust, so there's no point in trying to create a ...
The FAA's Flight Test Guide for Certification of Transport Category Airplanes that explains the various regulations notes:
For turbojet reversing systems intended for ground and/or inflight use, it must be shown that unwanted deployment of a critical reverser under normal operating conditions will not prevent continued safe flight and landing. Flight tests ...
You're asking about turbine (hot) reversers of early high-bypass turbofans.
flickr.com and twitter.com
It had the same mechanism as the cold bypass (blocking doors), similar to what the C-17 (right image) uses nowadays.
Lockheed L-1011 TriStar - Airliner Tech Vol. 8
It had target-type, but only during development.
Design Features of the ...