As a workaround on renaming PerformancePoint Database. After creating the service application with a GUID database l did backup the performance point database and reattached the backup database to SQL with a new custom name. To attach the new renamed custom database to the service application l did run this powershell command and l was able to delete the other database:
Set-SPPerformancePointServiceApplication -Identity “ServiceApplicationID” –SettingsDatabase “NewCustomDatabase”
Set-SPPerformancePointServiceApplication -Identity “ServiceApplicationID” –SettingsDatabase “NewCustomDatabase”