Yes, a BR30 bulb can fit into a BR40 fixture. However, there may be a small gap in the fixture due to the size difference between the two bulb types. This size difference may impact the aesthetics of the fixture but should not affect the functionality of the bulb.
BR stands for Bulk Reflector, that are traditionally for incandescent reflector lamps, not halogen Par lamps, which mean Parabolic Aluminized Reflector.
R40 is a Red Heat Lamp Light Bulb BR40 is a Clear Heat Lamp Light Bulb
Yes, but only the blue part can