@cacophony bro regarding sa pag change mo ng civil status from never married to engaged, I think it shouldn’t be an issue.
Pero if you would like to add your partner in your existing application, dapat married na kayo or in a de facto relationship (living together). If you get married after the lodging your visa, you need to update your application and inform the CO through changes of circumstances form 1022 before they make a final decision on your visa. You will also need to submit evidences of your relationship and additional documents related to your partner.