How would I insert one item into the user-edit page with templates?
Although you could add a button into the template, this is done better with the forms api using a custom module. You can use hook_form_FORM_ID_alter to alter the user_profile_form and only make the small change you want while leaving the rest of the form untouched.

As an example, you could add a button "My cool action" to the use profile form with the following code. You just need to replace MODULE with the actual name of the module you put it in.

function MODULE_form_user_profile_form_alter(&amp;$form, &amp;$form_state, $form_id) {
    $form['actions']['newaction'] = array(
        '#type' =&gt; 'submit',
        '#value' =&gt; 'My cool action'
    );
    $form['actions']['newaction']['#submit'][] = 'my_newaction_callback';
}

function my_newaction_callback($form, $form_state)
{
    // this function is called when your button is pressed
    // do whatever you want here.
}


Update #2

You could place the button in the middle or top of the page using the following code and figuring out which weight places it where you want. Try a weight of 0 to have it near the middle.

$form['newaction'] = array(
    '#type' =&gt; 'submit',
    '#value' =&gt; 'My cool action',
    '#weight' =&gt; -3,
    '#submit' =&gt; ['my_newaction_callback']
);