When creating groups for routerOS users (/user group add policy= . . . ), routerOS provide means for specifying the group policy.
What if I want to add custom policy? (e.g a group that prevent/limit access to the hotspot menu/submenus)

To implement, we can have a new type of policy called CustomPolicy. A CustomPolicy can contain either Allow list or Deny list of routerOS menus. e.g

CustomPolicy1.action = Deny
CustomPolicy1.item(0) = /wireless
CustomPolicy1.item(1) = /radius add
CustomPolicy1.item(2) = /hotspot user add

CustomPolicy2.action = Allow
CustomPolicy2.item(0) = /interface print
CustomPolicy2.item(1) = /radius add
CustomPolicy2.item(2) = /hotspot user profile print

This feature is available via the web interface by customizing the skins. Would be nice to be able to the same with Winbox though.