custom icons

As much as I like the plugin, I’d prefer other icons for “share” and “follow”. At the moment I exchange the mail.png and the rss.png in their directory by my own png-files, but I don’t want to repeat this after each update.

I tried to follow the instruction in the plugin’s readme.txt by adding a shortcode to each post, which results in two sets of icons: one my custom icons, the other the themes default icons.

My question: Where should I add this shortcode in order to substitute the plugin’s default icons by custom images?