The overrides chat tab controls messages about actions such as spell casts and which chat channel should be used, can be handy for telling the party or raid that the healing is resurrecting player x.
Using override settings will ignore the skin settings, making this an option to permanently fix settings to your preference.
For the skin settings see the Skins Chat tab
#s
is substituted with the spell name and #n
is substituted with the players name.