desktop file category keys, boolean, post-install

Hi,

I've a question about the choice for a good category key for xdg desktop 
files, based on a discussion here:

https://github.com/jackaudio/new-session-manager/issues/96

For that particular category (NSM) two keys are chosen, 
X-NSM-Capable=true and X-NSM-Exec=zynaddsubfx -I jack -O jack

The question is, if two keys are really needed or if one would cover all 
situations.

About X-NSM-Exec there is no discussion, but it's also argued that the 
second X-NSM-Capable is needed, because it needs to be a boolean with 
the following argumentation:

"It is important that this is a boolean value, so that it can be 
manually set to off if needed. (for example, user override of this value 
via local files as a way to filter specific entries; could be used also 
as post-install step in some projects where NSM/liblo is optional at 
build-time). So applications scanning the desktop files need to make 
sure to read the value and it be "true"."

Is this argumentation valid? Or can one also remove a key from the 
desktop file or just set the key empty (X-NSM-Exec=), to set it off 
manually or as post-install step? In that case one would only need one 
key for this category, which is preferable probably.

Regards,

Flomer