Can a chiropractor align the spine above an l4-5 bone fusion that was done 2 years ago?

Not in my opinion. I dont recommend manipulation after fusionthe stiff sgment can put extra stresses on adjacent segments while manipulation is well studied in normal spiines I am not aware of any in post fusion spine leaving results outcomes unpredictable in the post fusion spine post fusion spines are different.
Perhaps. Adjustments and manipulations can usually be done safely once the fusion has healed. If there is still pain in the area, your doctor may need to do studies to be sure it is healed. Let your chiropractor or physical therapist know your surgical history. If there is any doubt, ask your surgeon.