1.  You can use and modify the temp reports (alter and then Save As... to another location).  This is the smartest way to customize these reports and make them available to users if you wish.

2.  Don't even think about touching the Tableau Server db

• You'll immediately surrender support from Tableau and
• Nobody here will be able to help you
• It could have negative effects on other reports or internal tables with a cascading effect on other custom admin reports people offer here in the forums
• If Tableau changes its environment (which it is known to do) your work could become invalid or, most likely, break your Tableau environment

Sorry Sylvain, what you require is not possible

It is possible to change the admin views.  It is definitely not supported nor recommended.   The file you're looking for is:

<Version>\bin\vizql.war

Inside this zipped file live the templates used for the admin views:

\WEB-INF\views\admin\

tabbed_admin_views.ftl

tabbed_site_view.ftl

views.ftl

If I had to do this I would just change the Custom SQL and just pull in what I needed or didn't.  Crack those templates open in your favorite text editor.  Find the custom sql and make the changes you need.  You have to make sure that you call everything the same thing or else the calculations in your template will break.

This isn't a how to more a it can be done.  Nor is it for someone faint of heart. Took me ton's of trial and error and breaking the templates before I had a couple of things working.  So please use caution, don't use your production server, always have a backup, not supported, likely to break in the future, and once again not supported.

Best of luck,

Gerardo

While I understand taking on a challenge, sometimes it's best to just not open that can of worms