There is a push for atheist chaplains in the military. An atheist is a person who denies or disbelieves the existence of a supreme being or beings. A chaplain is an ecclesiastic attached to the chapel of a royal court, college, etc., or to a military unit. An ecclesiastic is a member of the clergy or other person in religious orders. Keeping all that in mind, there is no such thing as an atheist chaplain.
If atheists want advisers or spiritual leaders, that's fine! But those advisers and leaders are not chaplains. They need to pick another name instead of redefining chaplain. The thesaurus has many other words that could be used for the advisers atheists are wanting; advisers is one of them. So is guide, counselor, guru, mentor, aide, coach and consultant.
Instead of rewriting the dictionary, people need to simply pick a word that already fits.