<===> input.scss
.thing {
	color: black;
}

.a,
.b,
.c,
.d,
.e {
	&:not(.thing) { @extend .thing; }
}
<===> output.css
.thing, .a:not(.thing),
.b:not(.thing),
.c:not(.thing),
.d:not(.thing),
.e:not(.thing) {
  color: black;
}