I guess that would depend on where you are in the upgrade process. If you are still downloading then I would say no, it should be safe to stop it.
If you are at 90% + in the overall installation, then it's up to you how you proceed.
Did you back up all your critical data in advance?
Did you create a system / disk image in preparation for the upgrade?
https://www.windows10forums.com/threads/please-for-your-own-peace-of-mind.794/
We've seen any number of potential issues with the upgrade process and things that can go wrong, sometimes they are as simple as having a wireless Bluetooth dongle attached, other times it would seem to be more complicated and practically impossible to sort out.
Aborting the upgrade process may result in other problems, from which, you may be one of the lucky ones and simply have to set through a long roll back process or unlucky as in some other instances where folks have had to manually reinstall their previous OS