Does known_hosts support comments?

Yes. As the manual page for sshd notes:

Each line in these files contains the following fields: markers (optional), hostnames, bits, exponent, modulus, comment. The fields are separated by spaces.

[...] The optional comment field continues to the end of the line, and is not used.

Lines starting with ‘#’ and empty lines are ignored as comments.

This means that you can create comments in two ways:

# Comments allowed at start of line
closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net

The whole first line is comment and the closenet.example.net is also comment

not sure if this solves the problem, but you can alias the IP in your .ssh/config file with something like this

Host rememberme
    HostName 100.110.120.130