Oh , you’re right , i tried it only for one variation , since we’re dealing with variable product then field ids should be different.
My guess is you should do it dynamically some how
I mean you should create dynamic custom fields which is not possible with ACF (normally).
What you’re trying to do requires some programming. my solution to this is :
add an html field to variations box like this :
<input type="text" name="myfield_<?php echo $variation_id; ?>">
in this way all fields combine with $variation_id so they wont be the same any more
And to save the fields you can use save_post action
http://codex.wordpress.org/Plugin_API/Action_Reference/save_post
I hope this will help
