Add the new tree (The British Royals). User created with Member access to BR tree (visitor to live one which in effect means none.)
Admin > Modules
I didn’t care if the same Modules appeared in BR and that’s not where to access is set.
Modules > Menus, Tabs, Blocks, Sidebar, Reports
Each has 2 tabs representing the 2 trees. BOTH showed each setting set to visitor; my live tree had been customized and was reset to visitor in addition to that of BR which was set to visitor (or whatever is default).
[updated: 30 Nov 2021]
MacOS: 10.15.7 (Catalina)
Safari 14.1.2; Firefox 94.0.2
PHP 7.4.5 FastCGI; mySQL 5.x