Create an entity for each company. Create entities in system > settings
Add a new Entity
To add a new entity:
switch to Global Entity Scope in the dropdown (select and wait until page refresh)
in the same dropdown, choose Add New Scope (select and wait until page refresh, the new entity is created)
in the same dropdown, choose the new entity and select Edit Current Scope to change the name
switch to a scope to configure it's settings
Once the new entity is set, give users access to the scope(s).
A user assigned to multiple entities can switch between entities. Click on the entity name under ENTITY in the header, the entity dialog will pop up:
Overrule Default configuration
Configuration set on Global Entity scope is applied to all entities unless overruled by the entity itself (if the checkbox is unset).