This might be by design, but just in case it is not the following happens when you try to rename a discovery rule by just changing the case of the letters. If you try to update a Discovery Rule name from lets say "PROD" to lowercase "prod", you are given the following message: "Discovery rule "PROD" already exists.". You can get past this by adding something to the name and removing it. For example, lets say you update "PROD" to "prod2" then update it then go back and remove the 2 off of "prod".