Hi there!
Did you enter the command exactly as "r.SSBevel.Strength -4"? If so, you do not need to include the minus sign when entering console commands. In the documentation, it is only used to represent a placeholder value. Simply put, your final command should look like this: r.SSBevel.Strength 4
If you did enter the command correctly without the minus sign and it still didn’t work, please try using r.SSBevel.Strength 4 combined with r.SSBevel.Radius 4
This combination will give you a very obvious and visible effect so you can verify it is working.
I hope this helps! If it still does not work for some reason, please let me know and I will look into it to see if it is a specific bug.