If I do a 'Find in Files' I can fill in the 'Files' setting to limit search to a particular file pattern (fif_files).
However, if I put in '--exclude' and '--exclude-dir' parameters into 'Extra options' it won't work. This is because '--include' has to come before --exclude*, but Geany puts the 'Extra options' before the fif_files.
Simply flipping it around in the `get_grep_options` function seems to work for me.