Over time the filter list shown under menu 'Photo\Edit In' (or right click\Edit In) has accumulated redundancies which I wanted to take out. For example listed is Exposure X5 as well as X6 when only X6 is installed on my PC.
Is there a way to optimise/show only relevant filters?
Open the LrC Preferences and go to the External Editing tab.
In the second dialog area, Addition External Editor in the Preset: box click that, Select the one you want to remove, Select that drop down again and select "Delete Preset NameOfEntry".
Repeat to remove the ones you want to go away.