I would recommend looking at this in another way. With the latest version of Qlik Sense we offer the capability of creating variables. Here you can define an expression for the variable (sum(Sales) for example).
This can then be referenced from within another measure by using $() such as $(vExpression) where vExpression is the variable holding the new calculation which you want to use.
I hope this answers your question. If so, please mark this as answered and helpful.