menu type mainmenu override

I try to override the mainmenu. I always get output of mod_menu from T3 framework.
I read http://www.t3-framework.org/documentation/extend-com-content#isolate-template document

The file priority should be the answer but I cannot get the override correctly.

The purpose of override is that I want to remove the "nav navbar-nav" class of "ul" tag

Do I miss something?

May I get help from you?

T3 framework : 2.5.0
template: T3 Bs3 Blank
Joomla! : 3.4.3

Many Thanks
Martin