Oh and here is one way from the command line. Add the following lines to the format file and save as mandolin.fmt.

tablature #1 pitch=G, 28 0 63 m_head m_note
tablature #2 pitch=C 28 0 63 m_head m_note

command for mandolin:
abcm2ps -F mandolin.fmt -T1 [rest of command line]

for tenor mandola:
abcm2ps -F mandolin.fmt -T2 [rest of command line]

Alternatively (at least with development versionsofabcm2ps 6.5.0 or later) you can place your own tablature # line in the abc as %%tablature #1 and always call the command line with -T1.

(The folkinfo converter uses this second method mainly because there is a limit of 8 tablature # lines per format files. In most cases I want to offer a large range of pitches and some format files contain more than one set of postcript functions). I'd have a lot of duplicated postscript and format files if it used the first method I've given)