succesfully changed order regions in info file, but rendered html stays untouched Layout-wise I want 3 columns in this order: sidebar first - content - sidebar right. Since the region order in d7 is content - sidebar first - sidebar second I wanted to change that order in html. 

If I remember well, all that's needed to change the order of the regions, is to do that in the .info file.

So I simply just put the content region between sidebar first and sidebar second so the info file has the following in it:

regions[header] = Header
regions[highlighted] = Highlighted
regions[help] = Help
regions[sidebar_first] = Left sidebar
regions[content] = Content
regions[sidebar_second] = Right sidebar
regions[footer] = Footer


When I go to structure -> blocks The result that I'm seeings is what I was aiming for; the content region is being replaced. Yet, when I go and check the HTML,The order remains content - sidebar first - sidebar second.  

Goes without saying I cleared caches often.
the orders of your regions are probably defined in the page.tpl.php of your current theme. so you will have to change the order there, changing the order of your .info entries should (if any) only change the output from configuration pages.