Won't meet current code...once a vent, always a vent. When you start to use the vent as a drain from above, it is no longer a vent for below. Now, the stuff below isn't vented properly per today's codes, either. Your choices are: run a new drain line down, or a new vent line up. You can combine the vents at 42" above the new stuff (or 6" above the flood plane, whichever is higher) so you maintain one vent through the roof, or just vent it separately, if it's easier.