How many miles were on your car when you changed the fluid? I'm really nervous about anecdotal evidence from old-time mechanics that transmissions tend to fail after you change the fluid.
EDIT: Yes, please do post the video! I've been thinking of making a few volt maintenance videos myself, since YouTube is severely lacking for us DIYers haha.
From what I've read, it seems that most of the time those transmission failures tend to happen after a complete
transmission fluid flush on a particularly old transmission. Basically, if the transmission fluid has gotten black and burnt through overuse and a lack of regular maintenance, gunk can build up in the valve body channels or it's also possible that the clutch body has worn out. If the clutch body has worn out, then metallic flakes can be suspended in the old transmission fluid which, coincidentally, still help the clutch body grip. So, the thinking is that when you completely flush old burnt transmission fluid with new fluid, the new stuff can mix around the gunk in the valve bodies, potentially displacing it elsewhere that is very bad cause it can act like a dam. For the clutch body, the new fluid will not have those suspended metallic flakes, so it won't assist the clutches gripping.
So flushing transmission fluid can only be "dangerous" if you already have a damaged transmission or are running on old burnt fluid. I referenced this video: https://www.youtube.com/watch?v=o690DovjDAc