If you do need to modify your markers en-masse another option is to use
our MarkerTools plugin ..
One of its features allows you to export, modify, then import the
markers back into your files. If you do find some consistent problem
with the marker text, you may be able to use Perl of some search/replace
tool to process the exported marker list before importing. The 30-day
trial should give you enough time to clean up your files without needing
to buy it.