The good thing about the old pfile was that you could easily commenting out some parameter-values (resetting them to their original value) or add comments on changes made to the pfile.
In the SPFILE you can do the same:
To comment out a parameter-value (reset it to its original value) you can you:
ALTER SYSTEM RESET sort_area_size SCOPE=SPFILE SID='*';
To change a parameter-value and add a comment to it, use:
ALTER SYSTEM SET timed_statistics=TRUE COMMENT=Change due error 123' SCOPE=BOTH;
Parameters starting with an underscore should be placed between quotes
ALTER SYSTEM SET "_collect_undo_stats"=FALSE SCOPE=SPFILE;