Alter Emails before sending with plugin

Michael 0

Hello,
I want to alter the content of emails, before they get sent.
Therefore I subscribe to the MessageContentPanel.on("beforesendrecord", this.beforSendRecord); event. If I alter the Email in plain text mode:

beforSendRecord: function(panel, record){
      record.setBody(" ... my html text ... ", false);
},

it got saved, but nu as html:

record.setBody(" ... my html text ... ", true);

it doesn’t.
If I subscribe to the beforesaverecord event I can alter the HTML but get the error Popup “Do you want to save changes”.

Is there a way to alter the html body without the popup?