Good - thanks for the update. i will make 1 small pointer for you....
If in a service pack we make a change in this template, then we will have to ship it with the service pack.
So in this case if you made some changes to the file, you will loose them but you will get the latest version from 3CX. For example in the next service pack we have some new variables in the welcome email template. if you customized this welcome email template with your changes, and the next service pack is released, the updater will replace your customized file.
So you have to do the following:
1) We will not update files when no changes are made.
2) Your changes are not lost and after every service pack a rollback folder is created. Example: In my case in C:\ProgramData\3CX\RollBack
So you can follow the structure and take your "old" customized file from there.