You can alter the ejector geometry slightly but be careful as the part does double duty as the bolt lock as well. It must be free to ride the recess in the bolt to ensure the bolt can operate properly and not wear a hole in the side of the bolt. the exact angle must also clear the hump on the op-rod or the brass won't eject properly and/or be more damaged if you reload. Altering the mass of the op-rod changes the timing of the action and would require changes to spring energy and gas volume to ensure lock up dwell time and sufficient energy to strip and chamber a new round. You may also have to work out the variables in the travel of the op-rod since it's basically an unsupported part and the reductions would need to take into account any integrity degradation and angular travel that may cause the op-run to jump out of the receiver track during cycling. If you had access to the proper program, I would rather run these simulations on a PC than live fire experimentation. Even after that it would still have the ammunition and environmental variables that would influence ejection to include other parts such as the extractor shape, sharpness, spring force and cleanliness, as well as the bolt face and chamber condition which can allow the brass to be deformed just enough or drag just enough to change the variables again as the empty tries to extract, ride the magazine feed lips until the neck clears and then get to leave the nest without impacting any obstructions.
So before you do anything to change the rifle profile be sure you study it in great detail to ascertain the intended and unintended consequences of each modification. Once you've done that and everything works properly, you can determine the viability of a universal mod that others could use and get the same results.
My post is not meant to discourage you, just to help you consider how all the parts work together. The Mini doesn't have any unnecessary parts except for maybe the sling points, so as you focus on the small picture be sure to step back and see the big one as well. That will make your project successful.