Generally speaking, a command will support reading configuration information from a file only
if the developer(s) included code to support it. The developers for feh did that in a manner of speaking--see next paragraph. If the developers did not include that support, you would need to write a wrapper around the command to automate the process (e.g. read the contents of the config file, translate the settings to command line options, and then launch the command with the appropriate command line options). In essence, you would be adding the config file support yourself.
For feh, the man page says:
CONFIG FILE SYNTAX
The config file allows the naming of option groups, called themes. If ~/.fehrc or /etc/fehrc
exist, feh will look in them for name/options pairs. If neither of them exist, feh will create
a default one in ~/.fehrc.
It takes entries of the form "theme options ...", where theme is the name of the entry and
options are the options which will be applied when the theme is used.
An example entry would be "imagemap -rVq --thumb-width 40 --thumb-height 30".
You cane use this theme in two ways. Either call "feh -Timagemap *.jpg" or create a symbolic
link to feh with the name of the theme you want it to use. So from the example above: "ln -s
`which feh ` ~/bin/imagemap". Now just run "imagemap *.jpg" to use these options.
Note that you can split a theme over several lines by placing a backslash at the end of a line,
like in the shell.
You can combine these themes with commandline options. An example .fehrc is provided with a
couple of cool example themes.
So, if I am reading that correctly, you will need to pick a name--a theme name
--to represent a specific combination of options you want feh to use. Place the appropriate theme-name-plus-options entries in ~/.fehrc. Then launch feh with the theme name appropriate for the group of options you wish to use.