I haven't been in "The Book" in several years. When I still had my FFL, Removing or Altering the numbers in ANY way was a major NO NO. Understanding, as long as you plan on owning it forever, and I do mean FOREVER, you can do anything you want. Understanding, not even your decedents will be able to legally sell or transfer it in any way. Short answer is NO, you cannot drill through the zeros.
Coffinmaker
PS: Since I held an FFL, the laws have only gotten more stringent. The BATFE does not have a sense of humor. They also, DO NOT take prisoners. They (BATFE) are not, regardless of popular belief, there to "help" you.