i dont quit understand what you are trying to say, do you want to hide both the post reply buttons or do you just want to get rid the one above your username or just hide it?
if you just want to hide it in then in SHOWTHREAD template.
look for:
PHP Code:
<if condition="$show['largereplybutton']">
replace with:
PHP Code:
<if condition="$show['largereplybutton'] and (in_array($forumid, array (X,Y,Z)))">
just replace x,y,z with the forum ID(s) on where you only want the post reply to show