Plumbing vent pipe

can a 4 inch toilet vent line be downsized to a 2 1/2 inch vent line 4 feet before the line terminates. The house was remodeled and a addition put on and this is in the new attic section. i don’t have a picture.
any help is welcome.

P3113.1 Size Of Vents. The minimum required diameter of individual vents,branch vents,circuit vents,vent stacks,and stack vents shall be at least one-halph the required diameter of the drain served. Vents shall not be less than 1.25 inches in diameter. Vents exceeding 40 ft. in developed length shall be increased by one nominal pipe size for the entire developed length of the vent pipe.

thanks for the info i will add it to my inspection.:mrgreen: