This twig code will create a [Edit] link in user profile which will appear to the user only when he is viewing his own profile.Paste this code in a twig code element in user profile and set the price for editing nick=0 in the shop settings if you dont want to cut any pluses for changing nick.

{% if api.r.get('uid')==api.user_id %} <a href="shop.php?act=nickch">[Edit]</a><br/> {% endif %}