Messages (texts or emails) marked as a "Master" cannot be edited, however they can be copied and then edited. Here's how:
Message Manager
locate message or canned reply (text or email) that you would like to copy
click the copy icon (looks like 2 pieces of paper)
rename it
assign to a folder (to help you stay organized!)
make edits
save changes
go to campaign and select message in Message/Schedule section
Campaign (Appointment Reminder, Drip or Blast)
locate the campaign, click on name in blue
click on Message/Schedule
click the copy icon (looks like 2 pieces of paper)
rename it
assign to a folder (to help you stay organized!)
make edits
save changes
select message from folder and message drop down
save changes to campaign (top right)