Yes, I have:
1) I did attach a tail to the bolt to be able to cock it from the rear, so now I don't have to use the top knob to cock the marker. I guess you could buy a rear cocking bolt and use that instead.
2) I cut the cocking knob flush with the top of the marker.
3) Installed a BSA red-dot sight.
4) Threw away the factory stock and bought a JCS RVA Combat Folding stock ($50.00) that mounts in the lower tube of the marker. It has an RVA included. It is an excellent stock and very practical. It allows you to adjust its length as well as the up and down angle, so your sight picture can be adjusted with the sight plane of the red dot.
With these changes, a marker that was totally un-ergonomical, became human form compatible.