Just checking what I did in a friendly game tonight with Onyx CF to see what others think. I was running an Umbra Legates Lieutenant, and the unit natively has NCO. Each time I used the LT order to activate the Umbra, I was explicit that I was using NCO to activate the LT order. When I look N5, and the fluff around the rules, the fluff around the rule says that some one under the LT uses the LT order. I want to know in this limited circumstance if you all think this was within the rules or outside them. PS This was a great close game where I lost in the bottom of turn 3, so all players had a lot of fun.
We might need some clarification on what "fluff" you are referring to because I'm utterly confused. The "Sibylla Says" underneeth NCO doesn't seem to say anything of the sort. If the question is are you allowed to use NCO on a model who both has the skill and is your LT, then the answer is yes. And if the followup question is "does it still hide my LT" then the answer is also yes. NCO technically allows the user to convert the LT order into a Tactical Order for the NCO model. This wasn't exactly how it was done in the past and in the past it was a more direct LT expenditure. But since now it's a pre-conversion before use, technically you would declare to use NCO, convert into a Tactical Order, and then be free to use that Tactical Order much like a model with Tactical Awareness does. And since you're simply using the skill to convert the order, the LT order is never spent nor used in such a way that indicates who the LT is.
Accidentally replied instead of edited (it's 5am and I'm having trouble sleeping lol) Should also clarify that most people still shortcut the conversion process and just say they are using the LT order with NCO instead of explicitly saying they are making a Tactical Order. The main value of writing that it's a Tactical Order is just what you are allowed to do with it (such as activate a fireteam when a normal LT order can't do that).