:gs/a/b/
Swaps every occurrence, not just the first.
The :s for when the wrong piece appears more than once in the line: with the g in front, every occurrence is swapped at once.
It's how you repeat a command with twin arguments — copy a.md to a.bak, then b.md to b.bak — changing both ends together.
$ cp campo-a.md campo-a.bak
$ !!:gs/campo-a/campo-b/
cp campo-b.md campo-b.bak