[leni536]

Assuming the '_' characters are on the same column for all lines then vim's block visual is quite adequate for the task. If it's not the case then I don't know how multiple-cursor will help, you still need some kind of regex to put the cursors at the right places, don't you?

[akashakya]

ah, that was a bad example for so many reasons. slightly better example

  foo_bar -> fooBar()
  baz_car -> bazCar()
  some_thing -> someThing()

An even better example is doing the reverse

  fooBar() -> foo_bar
  bazCar() -> baz_car
  someThing() -> some_thing

You can put cursors at every line and then use subword movement to find the word boundary.

> you still need some kind of regex to put the cursors at the right places, don't you?

I didn't say it replaces regex. You need regex just to place the cursors. you don't have to write complex regexp edit text (as shown in this example)