Can I Simply Change A Transaction Log From Unrestricted to Restricted?
I prefer restricting to unrestricted.

If some process goes awry, then I don't want the log file to grow and grow and fill the disk up. I'd rather the DB stopped working than the entire Server/SQL Server Instance.

However, in this case you have a different issue: most likely "FULL" recovery and no log backups. Change to simple, shrink the log to, say 500MB, allow growth at 250MB, set a maximum of 2GB.