Hello!
I am a paid user of Directory Opus. One question that has always bothered me is, why can't the file extension be hidden in the App? In this case, it is easy to make mistakes when renaming files. Please consider adding this request to the App's improvement and optimization plan. Thank you.
It can be hidden. Folder > Folder Format > Columns: Hide file extension in Filename column.
(That also hides it for thumbnails mode.)
See Folder Formats: Quick Guide for how to make that the new default everywhere.
How can I do this universally; instead of folder by folder? Thank you!
See the last line in the reply directly above yours. 
This simple button script might help:
Set HIDEEXT=toggle
@if: Set DUAL=On
Set FOCUS=toggle
Set HIDEEXT=toggle
Set FOCUS=toggle