You can not purge styles in use, that incl. the current style because this style is in use...as the current style.
And there is one special thing, that normal BTN tools not handle:
Merging shouldn't be a problem (have you problems with merging, or just with clean/purging?
You can not clean/purge the first style in your drawing, normally it is the STANDARD style, but everyone is able
to rename style, also 'Standard'.
For example:
Standard is the first and Style1 a second one.
you can not purge the STANDARD style.
I rename 'Standard' to "AAA", rename 'Style1' to 'Standard',
now "AAA" is the first style and you can not this one (because it was and is the first style, just the name changed)
First style in your file is
Command: (cdr(assoc 2 (tblnext "STYLE" T)))