If I understand what you're asking, the screensaver would be the SETI GUI and people who want to run that but run it without the graphics, set the screensaver property to "blank" (meaning you get no screensaver at all - regardless of what it is).
If you want your own screensaver but still want to run SETI, then you need to run the SETI text client (the "CLI") instead. Then you can choose your own other screensaver (which will probably slow your SETI down, BTW.

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