There will be no change in the ATS state of a candidate's test attempt, if the cutoff score is changed after the test report is processed. The change in cutoff score will come into effect only for tests which are attempted after the change is made.
For example, let's say that the current cutoff score is 50. Candidate A has scored 60 on the test and has been marked as "Qualified". If you change the cutoff score now to 70, then this will not affect the status of candidate A. Candidate A will still be marked as "Qualified". However, if Candidate B now attempts the test and gets a score of 60, he/she will be marked as "Failed".
You can directly view the candidates who have qualified/failed from the test, by selecting the appropriate option from the reports section of the test as shown below -
List of Qualified Candidates:
List of Failed Candidates: