Flush cut the white PVC, a slip coupler and a small 1" or 3/4" will do the trick if needed.
By the image, I guess there's plenty of pipe to work with.
When placing the new bulkhead I would not glue it back; what I used to do is wrap some Teflon tape over the PVC and gently press it into the bulkhead then attach the assembly to the tank, silicon in between gasket, bulkhead and glass, then tighten with a plumbers wrench but not too tight.
There's a "specialized" tool, I believe name brand is Rambit to remove PVC from unions but is not worth the expense, bulkhead is cheap and so is PVC.
You may use a hack saw and cut the bulkhead perpendicular to the thread, heath the ABS plastic a bit; a heath gun is useful, then pull the softened plastic off the pipe assembly. I've removed glued PVC joints that way before but working from the inside; done it for pricey true-unions and whenever I have time to kill and no will to drive to HD.