How to create multiple measure simultaneously ( at one go )

Other than praying they add an api, the only thing I can think of is to do it in Excel 2016 (the object model lets you add measures), then import the excel file into PBI Desktop.

Object model method to add measures in Excel:

https://msdn.microsoft.com/en-us/library/office/mt574976.aspx 

Import into Power BI:

https://powerbi.microsoft.com/en-us/documentation/powerbi-desktop-import-excel-workbooks/