How to customize fvwm entries ?

[shaulk@netvision.net.il (shaul)]

My /etc/X11/fvwm2/menudefs.hook has the following entry for lyx:

[23:36:37 shaul]$ grep lyx /etc/X11/fvwm2/menudefs.hook 
+ "&lyx" Exec    /usr/X11R6/bin/lyx
[23:38:51 shaul]

I want to change it to 

	+ "&lyx" Exec /usr/X11R6/bin/lyx -width 631 -height 461

I tried to create a ~fvwm2/post.hook with that line. Which works.
But now my menu has to entries for lyx. The first one is the old entry, the 
one without the -width customization. And the second one is what I added.

How to get rid of / modify the original entry ?

						Thank you.