I created a button on pos.order linked to a server.action to update a custom field. Works fine but I would like to close the form automatically after the update.

I've seen there is the possibility to call a windows action to close it (ir.actions.act_window_close?) but I don't know how to add to my button attributes. 

Here's my (simple) code on form view to call the server action:

<button class="oe_highlight" name="616" string="kot" type="action" states="paid,done,invoiced"/>

How can I modify it without edit the py and xml files? I don't want to affect others databases.