It's not a fill hole, it's not even really a drain hole. It's the bolt that holds the damper rod and if you loosen it a little you can drain the oil through it even though that's not what it's for. It's really not going to work as a fill hole. Plus, whatever you do to "turn the fork over" is going to involve removing the fork legs anyway.
Once the leg is off you don't need to take it apart, you just need to remove the top cap. The spacer, washer, and spring come out. You turn it upside down and pump it while draining all the oil, add new oil, pump it some more to get the bubbles out, put the spring, washer, and spacer back, and put the top cap back on.
There seem to be a lot of questions. I know the original is a REALLY long post but please read it. Then read it again. Then leave it for a day, then go read it a third time. There's a lot of info there but it's all there. Take the time to read and absorb it.
Scott