Only on your PC? You can "Fool" your PC to slow down everything BUT YOU CANNOT FOOL other Player Gamespeed because they have their own client-sided settings.
It is not possible to do the sharinggan thing on your playmates since the thing that is synced are your current states, you will only appear normal at them. If you see them slow down, and that is not what is happening at them, then it is just like you are having "high download latency" and you cannot even aim properly at them because the locations they will be on your screen is not really the position sent by the server...
I do not think it is a good idea to do "slow-down" your GameSpeed since your playmates will gain advantage over you, and for me I dont like it...