Good lord, tl,dr. And I'm a dev. Client sure as hell wouldn't read all that. And I know this because at the start of my career I wrote those kind of long-winded explanations before I realized that nobody was reading them.

Brevity is a virtue.

"Dear client, the change itself took very little time but making sure that this change did not have unintended ripple effects took a lot more. We are careful and deliberate when deploying changes to your production application because in this mission critical application, downtime and errors are not acceptable. If you'd like more detail I can provide it during our next regularly scheduled catch-up."