Unfortunately, in GT7 it is not currently possible to properly enforce this via lobby settings. To set 100% power/weight for cars where PD applies a BOP, tuning would need to be enabled, even then there are caveats:
As of last week, there is an expanded option for BOP/Tuning, this is what I found:
If this is set to ON:
- The car will have the game's BOP applied (if it is Gr.1, Gr.2, Gr.3, Gr.4, Gr.B) or power/weight will be fixed to stock level
- All car settings will be fixed to whatever the game determines as BOP/standard, apart from the MFD options that you can change in-race
- The host can selectively enable options like Brake Balance, Anti-Roll Bar, Final Gear, etc. (this is new)
- Some other tuning options (like engine swap) can be enabled/disabled but these are canceled out by the BOP setting
- This ensures that everyone turns up in the same car
If this is set to OFF:
- BOP (Gr1-4, GrB) is not applied, settings aren't fixed
- The new setting where the host can selectively enable some car settings (like BB, Transmission, other settings) cannot be used.
- Power/Weight/PP limits can be set, but:
- All car settings can be changed according to parts that are applied to the vehicle
- Wide Body cars are enabled
- Some tuning parts cannot be prevented from being added, there is only "unrestricted" or "Extreme or lower"