act on vs alter

act on

verb
  • To affect something. 

  • To act decisively on the basis of information received or deduced. 

  • Το act accordingly to a (usually sublimated) desire or impulse. 

  • To take action against something. 

alter

verb
  • To affect mentally, as by psychotropic drugs or illness. 

  • To castrate, neuter or spay (a dog or other animal). 

  • To change the form or structure of. 

  • To tailor clothes to make them fit. 

  • To become different. 

noun
  • An identity or headmate of a person with dissociative identity disorder (previously known as multiple personality disorder). A member of a system. 

How often have the words act on and alter occurred in a corpus of books? (source: Google Ngram Viewer )