Tableau document a method for using URL parameters to open a view in the same window. Set Server Views to Open Links in the Same Window | Tableau Software
However this functionality isn't supported when the same parameter is applied through URL actions. Instead what happens is the url parameter is applied to the page your leading to rather than the page you're own. This results in the page you're on always opening by default in a new tab before you then have the ability to open a window in the same tab.
This creates limitations for example, I might have a url action that I'd like to open in the window I am currently viewing because it makes logical sense to stay in the same window ( same workbook or data ) however in other situations you might want to link to a new tab (sending user to a different workbook using url parameters to pre-filter that workbook). see image below for a possible implementation.
I initially thought this was a bug until Tableau support clarified that it was expected behaviour :
As discussed, the reason behind linktarget=_self opening
a new tab is due to the fact that unlike other parameters which apply directly
to the view being loaded ('embed=y', 'Category=Technology'), the linktarget
parameter controls the behavior of all links *within* the view that parameter
was appended to. So, a view opened using the URL
'http://host/views/workbook/view?embed=y&:linktarget=_self' will not
necessarily open in the same view. Instead, all subsequent links from that view
will open in the same tab/window.
In short, if a view is embedded with linktarget
parameters in the URL of the embedded code, any links from the view should
respect the linktarget. If linktarget parameters are added to a URL action,
that url will be opened in a new tab, and any links loaded *from* the new tab
should respect the linktarget.