Regarding the filetype ".INI" Wikipedia says:
"Semicolon (
at the beginning of the line indicate a comment. Comment lines are ignored." https://en.wikipedia.org/wiki/INI_file
Although a Mp3tag MTA textfile looks alike a standard INI textfile, it is not documented, that both filetypes are interchangeable.
One tricky way to add comments into a Mp3tag MTA script file can be as following ...
Action "Format value".
Field: MY_MTA_COMMENT
Formatstring: $char(0)'here is a comment line'
DD.20160530.1032.CEST