Replacing rusted metal front porch posts
Depends on what you mean by non-structural. I think it's very unlikely that the overhanging roof is self supporting as it seems to be a large span. More likely that the posts are holding some of the weight. 

Rather than replace the whole posts with something else (and altering the 'feel/look' of the place), what's your welding like? I only ask as the vast majority of the metal posts are fine. Cutting the 'feet' off each post and welding in new metal is not terribly time consuming and could be done one at a time negating the need for additional supports (handy since they are in pairs!).

I can't quite tell if the posts go into the concrete (hopefully not) or sit on top in some kind of foot. Maybe it's possible to make up some new 'feet' that can be welded/bolted into place with a little flair and ingenuity (after cutting away the bottom part of the post). Just a thought....