There is no problem to edit the COMMENT tag-field in all dialogs within Mp3tag.
Because the new edit field MY_COMMENT is a scrollable multi-line edit field, someone can view much more than 5 lines.
I do not believe, that someone, in a practical way, is able to put a multi line text into the standard "comment" edit field while in the dialog "Tag Panel".
Yes, it is possible, ...
- by using the edit dialog for the tag-field COMMENT within the dialog "Extended Tags", ...
- or when applying the "usrfields.ini" hack ...
Multi-line comment box
... which adds an additional multi-line edit field to the Tag-Panel.
'multiline=1' or 'multiline=0' is a ... 'yes/no'... 'on/off' ... switch.
DD.20150319.1104.CET