We are unable to replace an action bare with cat form stance and a modifier (CTRL) in the same time. I was in need to set some technique to a modifier key binding, but this action bar is enable for all stance.

This is a known issue, and one of those edge cases. While its possible to support, I've not really seen many people request it, in practice. I'd suggest this as a case where you'd want two bars set to switch in cat form, with one bound to the ctrl keys.