Use a "common" text box to fill-in values for Repeating Section textbox

Hi all,

I have something I want to do. I have a repeating section on my Nintex Form that has 2 controls (ex. "Currency" and "Cost").

I want to be able to set the "Currency" default value using a Common Textbox field that is outside the repeating section control. But I can still change the textbox value in the Repeating Section manually.

For example, I initially set the "Currency" to "USD". All new items in Repeating Section has the default of "USD" value, but I can still change them ("ex. EURO, POUND, YEN, etc.).

 Is it possible to achieve this? I'm trying to use Javascript but am having a hard time setting it properly.

Thanks!