Just about to transfer a pre bonsai Juniper into a bonsai pot. From what I've seen on YouTube, people cut off about two thirds of the roots then scape away most of the soli before planting. I'm new to Bonsai but this seems to be a lot of root disturbance. Will it survive?

Your plant is too young and immature to go into a Bonsai pot. Let it grow, create a good trunk first.

It seems to have a pretty good trunk.

And even without seeing the photo first my answer was right.

This is not a pre Bonsai, just a young plant. Do not put itt in a Bonsai pot, you will kill ir, no doubt. Do more research and learn how to grow a proper pre Bonsai and how ro prepare it for the future. Do not watch these instant Bonsai movies, look up lectures from real Bonsai growers.

Note that you do not have a juniper.

If you treat a cedrus like a juniper it will be dead before you put it in a new pot.

It is even on the tag.
Probably not a good choice for a beginner either.

Reminds me of an add on marktplaats. When I wrote to the seller that his juniper was not a pine he responded angrily; "junipers are pines too*...

Sorry I uploaded the wrong picture. I'm a bit confused. If were to take a nursery stock Juniper like the one below, couldn't I prune it, wire it and plant into a pot as per the instructions on this website below where it says it can be done from nursery stock?

www.bonsaiempire.com/blog/bonsai-starterkit

Different picture, same answer and nope, your plant is not ready to go into a bonsai pot. Unless of course when you want to grow a thin stick that's not ever going to be a good bonsai - if it survives at all.

Bonsai is a process of many years. They are not created instantly, no matter what movies may make you believe.

Also notice it is not a Juniper, and most important, the remark under the movie:
"and than continue reading this article for more in-depth information":
"You can prune up to about 1/3 of the total root mass"

That's UP TO 1/3. Not 2/3. In the right season using proper techniques on a plant that's strong enough to survive it.
Not a plant you just purchased and isn't even accustomed to its new environment yet.

What about a starter like here: www.bonsaiwarehouse.com.au/shop/bonsai-t...less-steel-scissors/

Isn't that a nursery stock?

In general, bonsai takes time. I would avoind first styling of a tree of pretty much any species, and doing rootwork. Effectively, you are damaging all parts of the plant. Think og it this way.. You will survive being malnourished for a few weeks. You will survive an amputation of your legs. HOwever, habing your leg amputated while being malnourished and not getting water will very quickly kil you.

The plants you are showing are all young plants. You can start with these. You can practice. But take your time. Do the styling this year. Then next year consider a repot. Or the other way around.