It’s a command-line tool but you can drag&drop Coalesced.bin onto Gibbed.MassEffect3.Coalesce.exe to export to JSON (it’ll create a directory called Coalesced). Once you want to repack, simply drag the Coalesced directory onto Gibbed.MassEffect3.Coalesce.exe and it will create Coalesced.bin (overwriting the original if present, back it up!).
Reply if you have any questions, problems, comments, etc.
If you’re less technically inclined, Monochrome Wench has a tool for visually editing data in Coalesced.bin