If you only want to edit the content of the notes, I believe it’s possible, you only have to find the corresponding file manually (they are in \XXXX subfolder - where XXXX is the code of the particular language version, e.g. 1033 being English - the files aswClnTg.htm/.txt for clean messages, and aswInfTg.htm/.txt for infected messages.

However, as David said said, the differentiation whether the .html or .txt format is used - is done automatically, you cannot change that.