New "EFI boot" drive appearing after reverting OS X drive to HFS+
To rename the Recovery Partition, falsely named "EFI Boot", I first mounted the Recovery HD, by showing all partitions in Disk Utility.
To show all partitions:
1.) quit Disk Utility
2.) In Terminal write or paste: defaults write com.apple.DiskUtility DUShowEveryPartition 1 and hit 'enter'.
Launch Disk Utility and mount the hidden, but now showing "Recovery HD" by selecting it in the sidebar and clicking the "mount" menu.  Here it did mount with its proper name "Recovery HD".

Then rename it by using Terminal and this command:
sudo bless --folder /Volumes/Recovery\ HD --label "Recovery HD",
or change the label "Recovery HD" to something that's preferred.

To revert Disk Utility's 'show all partitions' just use the same command with '0' instead of '1':
defaults write com.apple.DiskUtility DUShowEveryPartition 0

Edit: changes in macOS Sierra lead to a different approach:


Find the disk identifier by running the following command in Terminal:


  diskutil list



This will identify the Recovery HD with diskXsX (e.g. disk0s3)


Mount the Recovery HD with the help of its found identifier, e.g.:


  diskutil mount disk0s3



as in the example mentioned above in step 1, replacing "disk0s3" with your own found identifier.


Then use the following command for the disk label to change:


  sudo bless --folder /Volumes/Recovery\ HD/System/Library/CoreServices --label "Recovery HD"



Again, replacing "Recovery HD" for your own preferred disk label.