Carlos,
Being a retired cop I would want to know why this person wants to remove this number. That being said this number is on a ribbon panel that is attached to the shield. It is either a solid white metal or plated. The company who made this badge can do this in a snap.
Thank you for your concern same thing I told my local school district captain I don't know where he got the bright idea that I know how to engrave but trust me everything is legit no wrongdoing here. I believe this number is no longer in circulation in other words not being used one of the current guys damaged his and the wanted to change the numbers to replace the damaged one
Those badges are usually die struck from brass and then plated. The lettering is normally fired enamel filled that is done after polishing and before the plating.
You could carefully file down the area and soft solder another piece of brass over the top, engrave, replate and then fill the lettering with black Ceramit. If you are making enough money to make it worthwhile that is. Otherwise, you will pay some tuition for the learning experience.