Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.9)
// Compass (v1.0.0.alpha.20)
// ----

// Define a default map
$configuration: (
  "option": "default"
) !global;

// Define an empty map of custom parameters
$custom: ();

// Whenever a function/mixin needs the option map,
// Merge the custom conf to the default conf
@mixin test() {
  $options: map-merge($configuration, $custom);
  $option: map-get($options, "option");
  option: $option;
}

// With default values
test {
  @include test();
}

// Update custom map with your own options
$custom: map-merge($custom, ("option": "value")) !global;

// With custom values
test {
  @include test();
}

SassMeister-output.css

test {
  option: "default";
}

test {
  option: "value";
}