Gh0stnelax
Steampunker
You can - click on any item slot (to select it), and then click the number next to "Index: " on the right (in "Edit") tab to edit the item ID. For guessable reasons Terrasavr won't be able to display icon\stats for non-vanilla items, but it can manipulate them just fine, and you can assemble your own "libraries" of items by saving a tab and then loading it as a library using the button on the bottom-right of the item area.
Okay this really helped but i have encountered another problem, you see when modifying the character on a mod such as N Terraria, they have certain things extra for the character such as levels, skill points, and races, but whenever i use this it erases all that extra info reverting the character to a vanilla state making me start all over again, or atleast i would have if i havent backed my characters up xD