If a shortcut doesn't work as expected (i.e. as mentioned in the help text/manual) check whether you configured the same shortcut as global shortcut in System Preferences > Keyboard > Shortcuts. If you set up a "concurrent" shortcut it may also occur in Services, Screenshot etc.
Also check the app's preferences whether you set up custom shortcuts which override the app's default shortcuts.
It's not necessary to set up a custom shortcut for Word's Paint Format toolPaint Format tool double click.
The logic behind the Paint Format toolPaint Format tool button compared to the default shortcuts works like this:
- Choosing some formatted text and clicking Paint Format tool Paint Format tool (1st click) equals cmdshiftC (copy format)
- Choosing another part of the text ("2nd click") equals choosing some text and cmdshiftV (paste format) - the Paint Format toolPaint Format tool button is resetted afterwards!
- Choosing some formatted text and double-clicking Paint Format toolPaint Format tool and formatting several other text parts afterwards equals cmdshiftC and several cmdshiftV.
If you copy a text format/style with cmdshiftC (or with the 1st click on Paint Format tool!) it will remain in the "format/style pasteboard" until you copy another text format/style or quit Word.
You can apply it with Paint Format tool only once (2nd click) but with the shortcut as often as required.