To answer my own question above, since `-F` is applied by the regex selection, clearly those are not all compatible, so while the `-I` can go in the extra options as default, the `-F` can't.
I suggest a single configuration file option that has a list of values separated by `;` so `g_key_file` understands it and can help raed it. It would contain the base options and a pair for each setting in the order [here](https://github.com/geany/geany/blob/bc7e64f78f33ef867c9c1dfc2dc3ab76fd962ed1...) where an empty value means no option, so the default value is: ``` FIF_options=nHI;v;;i;;w;;r;;F;E; ``` It can be made visible in a single entry in `Preferences->Tools` that has lots of empty space so the entry can have a big explanatory prompt and locate it just below the `grep` entry.