Hope this isn't dumb question about Toro 570 Sprinkler Body - that is now missing the spray head ( nozzle ? ) - and has turned into a fountain instead of a lawn sprinkler.

Can I just unscrew the "guts" of old sprinkler body (the spring, pop-up, and seal) - and replace that with the "guts" of new Sprinkler Body - without digging up the lawn and removing the old Sprinkler Body's hollow plastic shaft ??

I bought a new spray head ( nozzle? ) to go with the new sprinkler body, so I can do it either way. Am just trying to save myself some digging, if possible.