New guys have no authority to do anything, certainly not to make law. It would take at least a decade for the most successful guy to have any impact, IMO.
A quick check on the ATF page shows that they're hiring for only two positions - and both are budget-related. You need significant turnover to get enough people in to make a difference. You can't infiltrate places that aren't hiring. You don't need 50% of the agency to believe pro-2A, just a small group - maybe 5% of very intelligent people who have the wherewithal to climb the ranks and get to a position to make policy changes.