replace null values with ‘0’ without changing the name of measures

There is two better ways to achieve your aim and without creating new measures:

1. Use format_string property in the measure properties.

The FormatString property accepts four arguments separated by a semicolon (;). The first argument is how positive value should be formatted, the second is how negative values should be formatted, the third argument is how 0 values should be formatted, and the fourth argument is how NULL should be formatted. The fourth argument is the one we are interested in! Here is an example of how I am formatting the Reseller Sales Amount: “#,##0.00;-#,##0.00;;0”.

2. use scoope statement in calculations tab :

   SCOPE([Measures].[col_]); THIS=IIF(ISEMPTY([Measures].[col_]),0,[Measures].[col_]); END SCOPE;

Visit : https://sqldusty.com/2014/07/15/how-to-display-0s-instead-of-null-in-your-ssas-cube-mdx-query-results/