Hi, I checked the source file
http://lilypond.org/doc/v2.7/Documentation/user/lilypond/lily-1721430265.lyfor the tremolo mark, but I don't see any special commands which make them
slanted as by default, the tremolo marks produced by Lilypond 2.7.27 are
perpendicular to the notestem if the note value is at least an 8th note and
is beamed to another note. I still don't know how to vertically move the
tremolo mark though.