Is there a utility to replace one block type with another within a region?

Question

I'd like to be able to select a region (either with a graphical utility or command line) and be able to switch one block type with another, e.g. change all cobblestone in the region to stone. Does a program/mod exist that can do this?

Answer 1

WorldEdit has such a command after selecting the area type

//replace [old block] [new block]

This will turn all of the first block from the area into the second block.

Answer 2

MCEdit has this capability. As an example, I made a selection that included grass blocks, and replaced the grass in that selection with cobblestone:

The tool that's selected in the first image is the find tool. Once open, there's an option to change it to find and replace. Then it's just as easy as selecting your two block types and hitting replace.