I have attempted the application of Hammerite paint several times. Regrettably, no layer of paint is capable of enduring the force of 100Nm or more exerted by a metal socket. Consequently, the painted surface quickly deteriorates, returning to its original condition. I have made minor adjustments to them (to the best of my ability) while in the vehicle.
I have resorted to using plastic cover covers, although I am not really like of them. However, they seem satisfactory. It is important not to misplace the little plastic tool that accompanies them, since it may be rather challenging to remove the caps without it, depending on the design of the wheel.
Matching the silver/grey colour with plastic caps may be challenging, although the colour is often sufficiently similar.