Question on importing via csv/excel Zephyr Scale

Is it possible to overwrite test cases via an import. That is reference the the test case in Zephyr using the key in your upload excel.

If so how does it behave? if you edit an existing step it should just update that step

if you add a new step will it add a new step ?

Is it possible to import parameters with the associated test case via excel? If so what is the format

Is is possible to import "call to test" test references in you test steps via excel? If so what is the format

If you have custom fields in Zephyr can these also be imported ?