Heading towards CIS-2020.

"...including, among other things, a ban on damage/defense calculators, and the use of any print screens/copies of the game screen before the game is finished..."

They forgot to ban the demon table xd
I won't ask why, I'll just ask if I understood correctly that if the opponent doesn't mind, all of this can be done?

You understood correctly. A specific pair of players has the right to agree on any changes to the rules, with the exception of the Rules of Fair and Respectful Play, the tournament schedule, and the rules for being in the hall and at the event.
The published rules are the default rules - precisely for those cases when it is not possible to agree.