Not fully validating, but adding them to yours config.ymlseems to do the trick:
Director:
rules:
'admin': ''
'fancyLongAdminURL': 'AdminRootController'
AdminRootController:
url_base: 'fancyLongAdminURL'
LeftAndMain:
url_base: 'fancyLongAdminURL'
The only thing I see does not work is the link myProfilein the upper left corner. But this is because the URL is hard-coded in a template LeftAndMain_Menu.ssthat you could create yourself.
Edit: The above should work just fine for the framework. For CMS and other modules, this should be investigated and more class / template overrides may be required, for example:
CMS , URL-
Intall_deleteinstallfiles.ss, AssetAdmin.js, VirtualPage.php,
SiteTree.php, AssetAdmin.php, routes.yml....Reports Report.php
URLRewrite , .
:. , 4.0:
https://github.com/silverstripe/silverstripe-framework/pull/3274