I would keep the dimensions of the plane and use the smaller propeller. The smaller propeller will weigh less, the wing loading will be less, the sinking speed will be less. The propeller will be a bit less efficient, more importantly, will turn faster and will run out the motor turns more quickly. If you are flying indoors, that may not matter much, since you don’t have the altitude to take full advantage of the energy available from the rubber. But once the contest is over, you can put the bigger propeller on for sport flying outside.
While formal Upset Recovery and Prevention Training in an aircraft isn’t required for pilots, CFIs must have spin endorsements moving forward, and Part 121 airline pilots are required to have UPRT in Simulator Training. Current Level D (FAA)/Type (ICAO) simulators feature upgraded motion to more closely replicate the sensations associated with inverted, skidding and other extreme flight attitudes. The Feds love AOA (Angle of Attack) indicators, and that may be one new requirement for Part 25 airliners. The market will probably demand AOA in Part 23 aircraft sooner than regulations do. Some VLJs have a defined UPRT as part of the Type Rating requirements.