Aksai couldn't refine his Spirit bloodline any further using his previous Spirit bloodline experiments after the completion of the transfusion process.
He wouldn't have been able to refine it any further after the bloodline origin had been decided by the primer liquid. Extracting more of the same bloodline origin from the druid's corpse and pairing it with vials of primer liquid wouldn't help.
However, the corrupted druid's bloodline refinement method was fundamentally different from that of Aksai's. It was related to triggering bloodline evolution or atavism. And since it was a Spirit bloodline, Aksai's very soul would also see some transformation.
