It would have required a complete redesign of the weapon. The BAR was designed to be heavy to handle the full auto fire it was designed to supply. This made the basic design impracticable for application as a general issue rifle.
Texas Bryan obviously did not understand the question since the M-1 Garand and the BAR fired the same 30/06 ammo.
It is worth noting that the Johnson rifle initially used by the Marines, was designed as a modular weapon system firing the same 30/06, but required a somewhat different design to handle the Automatic rifle role of the BAR, and while it initially was a better rifle than the Garand, it was much more expensive to manufacture and did poorly in the light machine gun role.