My question is whether, using the method and specifications that I'll describe, it's possible to write Python code to apply the given filters and perform the search?
400000000000000000 to 7FFFFFFFFFFFFFFFFF
........
Filtering Criteria:
We filter out all keys whose first four hexadecimal characters (prefixes) follow the pattern:
The first character is one of 4, 5, 6, or 7,
Followed by three identical hexadecimal digits (0-9, A-F).
Conclusion:
Applying this filtering criterion removes approximately 97.7% of all private keys within the specified range.
Yes you have done a big Mistake.
For each 3 hex character after first digit (4,5,6,7) there are total 4096 possibilities. Out of which you are removing the identical chars (total 16). That leaves 4080 still valid keys after each starting digit. 4xxx, 5xxx, 6xxx, 7xxx
That means you have to still solve 99.61 % of the remaining keyspace. Congratulations to Reality.