How to resolve error ORA-19802 when starting up an Oracle database instance?
Answer here: https://community.oracle.com/thread/2203255

reference answer:

You can always export, edit and import a pfile, even when the instance won't start like this:

SQL&gt; create pfile = '/tmp/pfile' from spfile='+DATA/rac/spfilerac.ora';


edit the pfile with the text editor of your choice and import back:

SQL&gt; create spfile='+DATA/rac/spfilerac.ora' from pfile='/tmp/pfile';**