Consider the sentence "Marcus spoke as a manager".
Imagine that Marcus was speaking at a company event, and he gave his speech as a manager, not as a coworker — as a representative of the company, not his private self.
To emphasize this aspect, one might say "Marcus spoke in the capacity (or role) of manager".
I am not sure if I master the English idiom perfectly, but I hope my point gets across.

Now, I would like to be able to add this emphasis in Latin, too.
The best starting point would be an apposition, I believe:

> 
> *Marcus dux locutus est.*  
> 
>  Marcus spoke as a manager.
> 
> 
> 

*Dux* might not be a good translation for "manager", but that is irrelevant.
But how to form a more emphatic version?
I imagine some of these might work:

> 
> *Marcus in/e munere ducis locutus est.*  
> 
> *Marcus in/ex officio ducis locutus est.* 
> 
> 
> 

I prefer classical Latin if attested examples are available.