How to apply manual changes in files?

[Dominik Klein]

I need to change a few hundred custom launcher-commands. This can be 
easily done with an sed script in ~/.config/xfce4/panel/launcher-<id>.rc

If I apply these changes while running xfce, they are not active right 
away and overwritten witht he old version when re-starting xfce.
If I edit the file while xfce is not running, it is overwritten with the 
old version the next time I start xfce.

What do I have to do to apply such a change? Using the guy is not an 
option, as this would take hours.

Thanks in advance
Dominik