It seems to work for most, but YMMV...sometimes you run into a store that will deny. People often do it with the F&F 20% off days as well.
If you qualify for the Seniors discount then you should just have to swipe your Optimum cars from there to get the points multiplier. They would have to tell you you’re not allowed to swipe your Optimum card.
Best approach is to say nothing, other than ask for the 20% off discount. From there just swipe your card and it’s automatic...don’t draw attention to the double dipping.