I checked an archived page:
http://rayshobby.net/opensprinkler/svc-use/opensprinkler-firmware-compilation-instructions-archived/
and looks like the fuse settings for OpenSprinkler 1.0 (using external programmer) should be:
avrdude -c usbtiny -p m328p -U lfuse:w:0xe2:m -U hfuse:w:0xd1:m -U efuse:w:0x06:m
to program a blank mcu, you can use the ISP headers on your OS 1.0. Specifically, carefully remove the existing mcu, insert the new mcu, insert your usbtiny programmer’s header to the ISP header, make sure the strip matches strip. Run the above command to burn the fuse bits. Once it’s burned, you can then upload a new firmware via:
avrdude -c usbtiny -p m328p -U flash:w:xxx.hex