The sap_hana_global_configuration ensures, that similar settings are defined onces.
During an installation the SID need to be set to the same value in different system roles using different variable names.
One way to get this solved is to use one variable for this unique content. For this we need to find a variable name which isn't used.
If we take the example of https://github.com/redhat-sap/sap-hana-deployment
The SID is specified with sap_hana_deployment_hana_sid.
If we want to configure https://github.com/redhat-sap/sap-hana-hsr we have to define sap_hana_hsr_hana_sid.
Asuming sap_hana_sid is not used, we can define it as group_var and add this variable as default to the systemroles.
If we would now set each parameter it will work as it was before. If we would add a variable sap_hana_sid to the group_vars/all.yml and add
sap_hana_hsr_hana_sid = "{{ sap_hana_sid }}"
sap_hana_deployment_hana_sid = "{{ sap_hana_sid }}"
to the default/main.yml File It would use the SID specified once.
This allows to use one global variable for the same content.