While this thread is a few months old, here is the code for my solution used for a current project. The code below gets the terms for the taxonomy called ‘commodity_codes’ and then updates the Search and Filter field ‘_sft_commodity_codes’ in my search forms by leaving the value intact for the query and simply updating the label to be a concatenation of the term name and the first 21 characters of the description with camel casing.

Thanks to the gist here: https://gist.github.com/rmorse/7b59b45a14b1ca179868

function filter_function_name($input_object, $sfid)
{
	if($input_object['name']=='_sft_commodity_codes')
	{
		//if we want to filter the options generated, we need to make sure the options variable actually exists before proceeding (its only available to certain field types)
		if(!isset($input_object['options']))
		{
			return $input_object;
		}
		
		//get the terms for the taxonomy
		$terms = get_terms('commodity_codes');
		
		//now we know there are options we can loop through each one, and change what we need
		foreach($input_object['options'] as $option)
		{
			foreach($terms as $term)
			{
				if($term->name==$option->value)
				{//we want to change the label for the option "black" - we can feed back in the count number to the label for this field type
					$option->label = $term->name . ' : ' . ucwords(substr($term->description,0,21));
				}
			}
		}
	}
	
	return $input_object;
}
add_filter('sf_input_object_pre', 'filter_function_name', 10, 2);

Hope this helps others.

— Tom @NPCrowd : https://npcrowd.com