This might be more work for whats possible and I would like roblox to add a system to add custom methods but currently this is the only way to do so and it involves metatables etc
Using a ModuleScript like @SirHammerWorks said is a good idea and an easy alternative to making methods for the Part class. Keep in mind that you’re going to need to instantiate a new BrickColor in the function if you intend to simply input the name of a BrickColor as an argument.
function Change(Part,Color)
if(Part:IsA("BasePart")) then --checks if the first parameter is a part
Part.BrickColor = BrickColor.new(Color)
end
end