Create subdomain of an existing record

I have this domain test.com, and created an A record for server.test.com.

The problem is that now, I want to make server.test.com a subdomain to be able to add TXT records specifically for server.test.com.

Will creating server.test.com as a subdomain cause problems for my existing A record ? Do I need to recreate an A record in the subdomain using @ IP ?

As already pointed out in the comments, there's no need for a separate subdomain, just add as many records you like for server.test.com.

Subdomains are needed when you want to delegate a subdomain to a different DNS-server, or you'd just like to break up a very large zone into smaller zones.