Change size of featured image in a post, without changing main theme

Hi there,
I have read several articles on this website about changing the size of featured image, but all of them where either making changes in functions.php
of the main theme (which is never recommended for maintenance), or using another plugin ‘Simple Images Sizes’ (which I try to avoid, since having too many plugins isn’t healthy).

Well, below I’ve come up with my own solution which seems to work in my website. I hope this could become useful to other users…

1) you need to use the child theme of Enfold

2) open functions.php, found in …../wp-content/themes/Enfold/enfold-child

3) in functions.php, paste the following code :

/**************************************************************************/
/* Change featured image size for "entry_with_sidebar"       */
/***************************************************************************/
function change_featured_image_size( $avia_config_imgSize ) {
	$avia_config_imgSize['entry_with_sidebar'] 	= array('width'=>849, 'height'=>566) ;  // big images for blog and page entries
	return $avia_config_imgSize ;
}
add_filter('avf_modify_thumb_size', 'change_featured_image_size' );

In my case, I wanted to change picture with a ‘entry_with_sidebar’ tag, but you might have to change that (other possible values are : ‘featured’, ‘featured_large’, ‘extra_large’, ‘portfolio’, ‘portfolio_small’, ‘entry_without_sidebar’).
Also the size I wanted was 849 x 566, but you might have to change that as well.

4) Once this is done, I think that you need to regenerate the thumbnails of each of your image, which can be done via the “Regenerate Thumbnails” plugin (which is a plugin that you don’t need after that, so you can deactivate after use).

Other than that, you should be good to go :-) !