You can get as many eyes as you want on all changes. I don't think it will help much. This sort of thing usually happens because of a change in something completely benign, rather than "security-critical changes".

We recently had a pretty major vulnerability exposed by a PEN test (thankfully) that was caused by a single misplaced NOT ! operator in a pretty simple function, maybe 20loc with 100% test coverage as counted by line.

The problem case was untested because while tests touched 100% of lines, not all combinations of paths through the code were tested.

The code had been written by myself about a year ago, and reviewed by four seasoned developers, none of whom spotted the issue.

How many thousands of eyes are on OpenSSL and yet major world ending vulnerabilities still crop up?

This might be a hot take, but you can make the process as painful as you like but at the end of the day, building secure software is nigh impossible. We should be putting less trust in software.