[{_id:"1",favoriteColor:"blue",updatedAt:123}]

db.collection.update({_id:"1"},[{$set:{favoriteColor:{$cond:[{$ne:["$favoriteColor","red"/** New favoriteColor value*/]},"red",/** New favoriteColor value*/"$favoriteColor"]},updatedAt:{$cond:[{$ne:["$favoriteColor","red"/** New favoriteColor value*/]},new Date(),/** New $updatedAt value*/"$updatedAt"]}}}],{upsert:true})