Is there a macOS equivalent of the Windows assoc command? I am looking to change a file association on the Mac using some sort of script. I know that I can do something like that in Windows using the assoc  command.
Is there something scriptable on macOS which will do a similar job?
No. Apple file mapping is implemented very differently than windows does it. The file metadata has many variables that affect launch services and mapping a particular file to a particular app.