Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.0.rc.1)
// Compass (v1.0.0.alpha.20)
// ----

.outer {
  color: red;

  .inner {
    color: green;

    @at-root {
      #{ selector-replace(&, '.outer', '.outer .foo') } {
        color: blue;
      }
    }
  }
}

.bar {
  .button {
    border: 1px solid;

    @at-root {
      #{ selector-replace(&, ".button", "a.button") } {
        text-decoration: none;
      }
    }
  }
}

SassMeister-output.css

.outer {
  color: red;
}
.outer .inner {
  color: green;
}
.outer .foo .inner {
  color: blue;
}

.bar .button {
  border: 1px solid;
}
.bar a.button {
  text-decoration: none;
}