Re-marking a surplus HK p7/PSP??

Not trying to create a counterfeit civilian HK P7 pistol, but I was wondering if it is possible or even legal to remark my German police surplus pistol's slide with the common HK commercial markings/date code and proof markings?? If possible, who could do this type of work, to include filling in the old police markings?? I have no intention of touching/altering the original serial number, which is illegal. I've seen Colt civilian AR rifles remarked to either M16A2/A4 to mimic their military rifle line-up.

Also, I'm hoping to refinish my pistol in a flat "HK" black as well.

The main reason for this request is that I want my surplus P7/PSP to match my civilian HK P9S/.45. Both of these pistols are keepers and will never leave my collection!!

Thanks for any info!!