The order of how the features.conf loads #include files suggests that adding that option to :-
/etc/asterisk/features_general_custom.conf
should override any incorrect setting stubbornly remaining in
/etc/asterisk/features_general_additional.conf
I know that @jfinstrom said that previously, you will need to do the rasterisk -x "reload" thingy to set it of course , I would be surprised if that didn't work . . .