sure, in blog view or grid?

open tpl/function.tpl and search for line 44 for grid view
replace this

<li><a class="linkedin_share" href="#" data-url="{$post.absolute_url}"><i class="fa fa-linkedin"></i></a></li>

to

<li><a class="tumblr_share" href="#" data-url="{$post.absolute_url}"><i class="fa fa-tumblr"></i></a></li>

and open assets/js/front.js and search for this

    $('.linkedin_share').on('click',function(){
        popup('http://www.linkedin.com/shareArticle', {
          url: $(this).data('url'),
          title: $(this).data('title'),
          mini: true
        }); 
        return false;   
    }); 

then add new one with the links and vars of tumblr or instagram