Since EZA has to go back and manually approve your article once you edit the resource box, would Google and the other search engines see this as a new article once it gets re-approved and knock you down in the rankings? Also, are you given a new URL so your backlinks would not work anymore? I tried submitting a ticket to EZA to ask and after waiting 2 days for a response all they could say was "We have no control over how the search engines index us." which is a very generic answer and I'm sure they know more information than that. Any of you more experienced article marketers know the answer to this?
Have you done this yourself and been OK? I would assume everything stays intact but I just don't wanna take chances since I've been building heavy backlinks to these articles for a few weeks now.
I have done for my article. 4 times, I have changes my resource box over my eZine Article but, I never felt ranking fluctuation with this stuff.
I have also made changes in my resource box content without much difference. I feel it does not have a very big effect , as you are worried about it.
ranking changes over time, i think you have a very long periond to test this out. so just try it yourself and make a conclusion.
I would say the content of your article affects your ranking more than the resource box. keyword density,relevance etc.