The best discipline at this age is distraction. You've taken the first step when you let him know what you want him to do. The next step is to give him something that he can do. In this way you are teaching him how to manage his own actions.
When he's doing or about to do something you don't want him to do remove him from the place that he's at and give him something else to do. For example, reaching for the outlet. Tell him "no touch" just as you're doing now; then turn him around and away from the outlet and give him a toy.
When he's pulling your hair while you're changing him, tell him whatever you usually say, and then give him something else to do.
As for diaper changing you could vary the toys that you have available when you do so and give him one or two of those that he can play with while on his back. Perhaps you're already doing this. I've found that singing silly songs while touching his nose or his feet etc. helps. Any move that surprises them can help too. Distracting them from their goal helps them be able to do what you've asked them to do.
My grandchildren are 5 and 8 and I'm still sometimes able to distract them with a quick tickle to the knees or ribs. It breaks their focus from insisting that they do what they want to do. I have to quickly go on to what I'm wanting done before they stop giggling and go back to their stubborn, "no," stance. This works less often as they get older and only works if I can let go of my frustration and anger. The tickling helps me to calm down too. I've found that the more intense I am about demanding that they do something the more stubborn they get.
I don't remember if tickling worked as well when they were 8 mos. old. Seems like it might have gotten them moving more so that it was difficult to change the diaper. But it did work when I wanted to get them to think about something else.