in skins//customer/addons/my_changes/hooks/buttons/custom.override.tpl use
{if whatever condition if you have if any}
{include file="buttons/go.tpl" but_name="search.results" alt=$lang.search}
{else}
src="{$config.full_host_name}skins/basic/customer/addons/my_changes/images/icons/go_custom.gif"
alt="{$alt}" title="{$alt}" class="go-button" />