The elmination of the word "a," an article, is completely voluntarily; either its inclusion or removal is solely the purview of the author. Coming from the school, that less is better, e.g., be pithy if one can be, "such procedure," is as correct and refers to the same thing as "such a procedure."
A common example of this, used by many, is "as per." For example, "as per your suggestion" means the same thing and refers to the same suggestion as the phrase "per your suggestion."