God Save The Queen,is the national anthem of Irish people living in the six counties,some of them undoubtedly would want to change it[who can blame them].
In the event of a unified Ireland are there going to be two national anthems.
neither side can expect to impose either anthem on the other side.
Irish people in the republic would be outraged if God Save The Queen was imposed on them.
logically it is equally outrageous for the Republic to impose the Soldiers Song on Irish Ulster Protestants.
At the present moment the Soldiers Song is the National anthem of the republic,not the whole island of Ireland.