I use my Powerbook G4 as a work laptop, so I am often pushing configs to/from network gear via tftp. In OS X 10.2.* I was able to easily start/stop tftpd with inetd. I would do the following:
1: comment/uncomment the tftpd line in /etc/inetd.conf
2: kill -HUP `cat /var/run/inetd.conf`...