Anything that is a safety improvement is acceptible, ie: Disc brakes, seatbelts front and rear, 12volt conversion, Wiper improvement, radial tires ect.
The mod plate is a recent development for currently the 49 and prior but they are woking on it!
I believe it was the Mustang and thuderbird clubs that fowarded the Modified plate towards ICBC and currenty are trying to make the status to 1970 and prior.