You can't do it with Persistent Search Filters but you could setup your own File Name preset. It's an undocumented feature but basically if you edit the file_preset.xml file you can create your own custom preset:
To add this new No EXE/DLL custom preset requires two steps.
Step 1 - Add preset to file_preset.xml
Open the file
C:\Program Files\Mythicsoft\FileLocator Pro\config\file_preset.xml and add this at the bottom.
<dosexp>NOT:*.exe;*.dll</dosexp> section provides the 'persistent' filter to exclude any file with the extension
.DLL and the
<attribs>-d</attribs> excludes all directories.
Step 2 - Add the language resource
Step 1 referenced the language resource 1000, which doesn't yet exist. This is what will be displayed in the UI. Find the language file you're using, e.g.
C:\Program Files\Mythicsoft\FileLocator Pro\config\lang-en.xml
and add this as the last language resource:
<res id="1000" text="No EXE/DLL" />
Now when you run FileLocator Pro you should see your custom preset. Anything entered in the File name field is now considered as a Boolean expression.