Configuring a Required Labeling System 
Prerequisites
If you want to work with alternative labeling systems you must first make the following settings in Customizing for Plant Maintenance (PM) under Functional Locations:
If necessary, define the labeling system as unique. This means that if you want to use a particular label in this labeling system, it is first checked whether the label already exists in one of the other labeling systems. If this is the case, the label cannot be assigned.
Procedure
Assign a new number and a description for the new entry in the user profile.
Result
You can now create functional locations within the required labeling system. When doing this, the system automatically proposes the labeling system linked to the structure indicator.
You can change the selected labeling system at any time either by selecting another entry in your user profile or by creating a new entry.
The labeling system selected in the user profile overrides the primary labeling system (which could be a cross-client setting).