Let me be clear to say: I do not suggest anyone try this.
But, I can say for certain:
An RV 6 slider can be opened in flight without catastrophe.
Here is my experience: My friend who built the 6 said from his experience that if left open on takeoff, it won't budge either way.
On accident, I took off with the slider cracked. After climb out, I tried to close it. It would not budge either direction.
But, as I am also concerned with egress from a forced landing, I tried an experiment.
On very short final, 70 mph, i opened the canopy. It was not difficult to open at that speed. I did not have any pitch deviations. But what was very noticeable was the increase in drag. I think I even had to add a bit of power to offset.
My take away: it can be opened easily inflight at approach speed. But expect substantial increase in drag.
I have tried to come up with a wedge to shove into the track to keep it from slamming closed on impact, but have been unsuccessful in finding something.
If someone has an idea of some type of wedge, I'd be interested.
Again: I do not recommend what I did.