Hi,
Is it possible to “challenge” a friend that also compete in XMAS rush.
we are far enough apart in the rankings to never meet each other. But it would still be fun to see how much the higher rank player beats the lower. 
Note, I´m the lower rank.
You can delete the boss agent and add your friend instead. However you can only add them if they are in your league or a lower one.
If they are in an upper league, you need to use extensions like CG spunk or CG Enhancer to select their AI since it is not available by default.