Just an update after some testing today...
if (BLESetCCCD1) ... (produces warning: "enum constant in boolean context")
The next bit along, i.e., for enum 0x40 needs comparing of course, therefore: "if (properties & BLESetCCCD1)"
Also, unfortunately, this fix only works for BLECharacteristic, e.g., BLEIntCharacteristic and BLEFloatCharacteristic crash the board immediately after compiling is complete (requires double button press to put into bootloader mode).
Furthermore, simply by only changing "_cccdValue(0x0000)" to _cccdValue(0x0001) crashes the board when not using BLECharacteristic (i.e., using the official master files, but with just this 1 digit changed)
I'm only working with arrays of data anyway, so I'm happy to continue using this as a temporary fix, but having the option to set the CCCD value properly would still be nice.