There aren’t any filters or actions that can be called to modify the element with class='acf-row'. If that’s the element you mean, there is no “.row” class in ACF. So yes, the only way to do this is using JS.
The only possibility you have to alter that would be to use 2 acf/render_field actions, one before and one after acf renders the repeater. You could use a PHP output buffer starting the buffer before the repeater is rendered and then getting an altering the buffer contents after. However you’d need to parse the html that ACF outputs and figure out how to update the each row class. Probably possible but potentially an nightmare to do.
