Not necessarily...If he became a Prime, he would pretty much be Optimus Prime thus defeating the point of calling him Optimus Primal to seperate the two as characters
There have been some deviations in the Prime naming scheme, such as Prima and Primon.
Another possibility would be if he were to be called "Primal Prime." Sure, it was used for another character in a different context, but only in one continuity that I'm aware of, and I'm sure Hasbro would be more than happy to keep the trademark.