When my brother married his second wife she refused to promise to obey & he didn’t want the til death do us part because he had already promised that one & the bish didn’t die. So, the vow with his 2nd wife was ”to love, honor, & be best friends for life”. Don’t know IF it just took the pressure off or what but they’ve been married for 25 years. It will depend on the minister as to changing the vows; but, writing your own vows has become commonplace..Shouldn’t be a problem.
Living together is basically the same as a trial marriage.