I have done so and Cloudflare recognizes those as the set name servers. BUT Cloudflare won’t activate my account with those name servers in place. It seems to demand that I use the default name servers that are assigned to every account.
There are two ways to setup Kajibi. One essentially has the domain added to their Cloudflare account, and you manage everything on the Kajibi control panel. The other has the domain on your own DNS provider, and you add MX and CNAME records as specified by Kajibi.
You cannot have a domain active in two different Cloudflare accounts at the same time. Pick one method or the other.