Altering font

[Thies Albrecht]

Hi everybody!

Currently I'm dealing with extending/altering lily's music font 
according to my needs. Now I'm stuck with the following:

I want to alter a symbol, e.g. the notehead noteheads.s2. To do so I 
open feta20.pfa from /usr/share/lilypond/2.10.5/fonts/type1 in FontForge 
(v20061220), choose symbol noteheads.s2 by double-clicking on it, alter 
it, close the window and then by choosing File -> Generate Fonts... -> 
PS Type 1 (Ascii) save it again to .../type1/feta20.pfa. When I process 
a file containing for example

\relative c'' {c4 d e f}

I still get the old notehead symbol.

Why doesn't the altered symbol appear? Can anyone give me a hint/link? 
Are there any other steps I have to do? Is it somehow not that easy as I 
think it is to alter/extend the existing font?

Kind regards
Thies