Measure logic for different hierarchy level

There is a formula in DAX called HASONEVALUE(<columnName>). This will return true if the <columnName> mentioned in the formula returns one single value. I think you can use this in your measure as a boolean condition to determine which formula to use for calculating the result.

For example

Result = IF ( HASONEVALUE(Product),
  <product-level-formula>,
  <customer-level-formula>
)

This means, at the product level, HASONEVALUE(Product) will return TRUE as a result based on the current product and at the customer level, HASONEVALUE(Product) will return FALSE because there will be multiple products.

For example, consider the following table.

CustomerProductQty

Result =
IF (
    HASONEVALUE ( Tables[Product] ),
    SUMX ( Tables, Tables[Qty] / 2 ),
    SUMX ( Tables, Tables[Qty] )
)

This measure will give the following result.

If you notice in the image above, the Result column is calculating differently at Customer Level and Product Level.

At Customer-level it is adding up the Qty field. But at the product level, it is dividing the Qty field.

See if this function can be used in your case.