I’ve had this issue with Preview and Graphics Convertor…
because SU uses a temp directory for the image, other apps can only edit copies…
to get around this I find the temp folder from Ruby Console in SU using this code…
%x[open "#{Sketchup.temp_dir}"]
when it opens in Finder, I drag it to the sidebar for easy access…
after editing, I use ‘Save As’ and navigate to the sidebar folder and select the stored version and select ‘Replace’…
there may be an easier way, but it works…
john