@tom81
I now catch the point.
You can’t change it smoothly due to peertube and you can’t keep it since you move out yunohost ecosystem.
That’s not easy
As you can see here there are no so much answers to your request, this is a forum people are answering if they can and if they want 
Spoiler : i have no real answer for you.
Disclaimer : i am not part of official yunohost team, only a user and contributor.
I don’t know if there is such thing like a tutorial or even tools to migrate out from yunohost.
Keeping yunohost domain name is not a solution if not keeping a yunohost platform.
It is clear that with 10.000 of video you are not in an personal usage and more at professional side. Your request here is to move from amateur to professional and if you don’t have the skills yourself it will be really hard to get real help without actualy paying professional to do it.
Yunohost is self hosting so you are in charge of quite everything and especially when moving out from it. To be fully independent relying on domain you own is the key, by choosen to have have your own domain you are for sure relying on yunohost entity.
Yunohost domains like noho.st are actualy one of the convenience offered for free to simplify life of self hosters, so i don’t know how it works when you want to move out. This service has for sure a cost and, those domain are owned by yunohost entity and paid.
There is a very long thread in this forum to request for reset domain names.
An automatic method was set with a initial password to be able to operate it without bugging operators.
The code is opensource so nothing is hidden.
Technically it is doable, but for the community this is to twist the purpose of yunohost offered domains, and this should be discussed somewhere else ( ie not with me ).
So perhaps move can be different …
What is your current bottleneck ? Network latency ? Storage ?
I would personally go to create a new instance with a new name and migrate slowly from one to the other with agreement of my users.