Can I overwrite a setting within sshd_config with a duplicate setting

No.

You could simply test this by adding the line and checking whether you can log in. Then you could comment out the first occurrence, restart the service and test again.

Reason: OpenSSH servconf.c has function

• process_server_config_line() on lines 1200-2171 (for 7.9p1)
• refactored to call process_server_config_line_depth() on lines 1260-2371 (for 8.3p1).

All global directives are processed only at startup and global directives are only processed once. The setting will stay as it was on the first occurrence.

On the other hand using the same directive twice may lead to misunderstanding.

Please reconsider parsing the file. You could also replace the whole file, if applicable.