 "Deck the Halls" ending
"Deck the Halls" ending    LALALA
Switch magazines, maybe   RELOAD [magazines are often mistakenly called clips]
One often follows a bullet    ITEM [in a bulleted list] 
 Three less than once
Three less than once    OCHO [in Spanish 
once  means 
eleven and 
ocho means 
eight]  
Despite my distaste for foreign words in English puzzles, given the cleverness of the clue, I'd go with it, especially given that OCHO is crossed with easy words.  I appreciate that DOS was clued not as "Two in Mexico" but the more clever "
Suggested actions."  

I have a hunch there is a covert theme, but it is beyond me.  I see SPERM..., DNA..., and BLOOD...; they're related, but AUTO... it's a prefix for an antibody produced in one's own bloodstream. 

SITPAT, even if it can be found in some reference or other, is at best outre.  The idiom is "stand pat." 

I just realized that there is a tomato in automaton.