Read the BDD style acceptance tests that were written during development.
This is the one chance you get to preserve that knowledge when it fresh and correct. Asking someone three years later (even the original dev) is no substitute.
Oh, and you can also run the tests to ensure correctnes.
You should know, that by removing all alcohol, caffeine and sugar, red meat, bacon, eggs and sausages from your diet, you can get rid of what joy you have left in your life.
This is overcomplicating something simple for dubious benefit. Just write a concise subject line for the change and short description or a list of bullet points what you changed/added/removed and why.
Not everything has to have rules for some regular format.
If I recall correctly, a certain amount of CPU, memory and processes has been reserved for root for a long time on FreeBSD. This would prevent the from bomb from exhausting all resources.
We will learn this the hard way.