More thoughts on your sight.
First off, remember, "there are no dumb ideas". At least that's what they say in the meetings where I work right before someone comes up with a dumb idea.
Anyway, If the screw goes thru small hinge loops, the idea of slightly (very slightly) squeezing one of them closed with something like a pair of locking pliers, still might work.
The idea here is to make the inside diameter of the hinge a very slight interference fit with the screw shank going thru it. If you squeeze the loop closed too much, you won't be able to reassemble the sight.
Ready for another dumb idea? This idea also is for designs with the screw going thru the hinge loops on the sight leaves.
You would remove the screw and sight leaves. Apply a little amount of Silicone Rubber (like bathtub calk) to the inside of the hinge loops with a toothpick. Be sure to apply enough to thoroughly wet the inside surfaces of the loops. Also apply a wet coat of Silicone Rubber to the outside of the screw body where the sight loops will be. Reassemble the sight. The idea is to have the slip fit joint surfaces coated with wet adhesive.
Let the Silicone Rubber cure overnight.
The next day, move both leaves to break the bond between the rubber and the metal. This might take the use of a screw driver or some other prying tool, but it should break loose fairly easily.
This (in theory) will leave the cured but now unbonded rubber in the joint which will permit you to move the sights from the down position to the up position using just a little force. They should (in theory) stay where you leave them unless they are pushed to the other position.
An advantage of this "rubber idea" over the "squeeze the hinge loop closed" theory is there is nothing you are doing that can actually break the metal or make it impossible to reassemble the sight. The Silicone Rubber also won't keep you from disassembling the sight if you want to.
NOTE: This idea relies on the fact that Silicone Rubber has a very low shear strength.
DO NOT USE EPOXY or some other strong adhesive. If you do, you will not be able to move the sight leaves ever without applying a LOT of heat and force.
If the design is something other than the "pin or screw thru the hinge loop" style, I would have to see what its design is before making any more dumb? suggestions. :shocking: