If this defect is encountered please change the back end file manually.
1) change something in the body area of the e-mail you would like to customize
2) then click HTML button if it does not work you may enter a unique number,
3) save it,
4) open shared.storage
5) search for the unique number you saved
6) and change the html text manually within the shared.storage file
7) save the shared.storage file
Try another browser.
Waiting for fix is a future release of Password Manager