Convert Subdomain CNAME Setup to Subdomain Full Setup

I am not experienced so much and as far as I understand, you have a CNAME type record and want it to be A type record?
Or, I maybe misunderstand the part “subdomain CNAME to subdomain Full”.

Keep in mind the SSL settings when doing so.

Hopefully, you would not get into the issue of this below:

I assume, if the domain(s) are at Cloudflare, you can setup multi-account and add a sub-account to manage them, if needed.

https://support.cloudflare.com/hc/en-us/articles/205065067-Setting-up-Multi-User-accounts-on-Cloudflare

I believe if using BIND, you can import a text file to Cloudflare DNS dashboard so you can easily do it (instead of clicking).

https://support.cloudflare.com/hc/en-us/articles/200168856-Importing-and-exporting-DNS-records

Alternatively way would be go programmatically through the Cloudflare API as detailed on the link below: