The fact slack doesn't allow you to lock down name changes must be such a gaping security hole for big companies. Change your name to the CEO, and profile image to match. Odds of people noticing the difference are extremely small until it's too late. Changing to slackbot seems like small fry!
At the same time the ability to change name is sich a godsend. We're currently abusing it to have presence info straight in the display name (e.g. mike-2/12~16vac.) to let anyone contacting us what to expect for response times, or wether to ask for a task if it's a few days before a planned vacation. Nobody seemed to look at the actual status property and it beats going to the calendars to check.
Looks like mike-2 is a robot powered by a doorbell transformer.