Covexin 8

When and why did they change the option to use covexin 8 IM to SUB Q

I do not know but I have never used it IM and I have used it for several years.

I'm a veterinarian.  Have not given a vaccine/bacterin of any sort IM to cattle in nearly 40 years... all subcutaneous. 
Probably has been 20+ years since I gave any injectible product (antibiotic, dewormer, etc.) IM, except for Estrumate/Lutalyse and cystorelin. 

Subcutaneous is the way to go, whenever possible.  I suppose... you're worried about a lump/knot on your show animal.  But... doggone it, they are ultimately a FOOD animal, and if you create a big abscess or area of fibrosis in a cut of meat... it reflects badly on those of us who are following BQA tenets.

Yes and no about the show animals getting absesses. I used it for years IM and just this spring I noticed that the box said sub q, wS just wondering when they changed the box. It's obviously safe for the animal to do it IM, I guess they just changed it because of the cuts of meat right?