I’d suggest using LESS’s escape function, i.e.:
a:link, a:visited {
color: green;
opacity: .5;
font-size: 1em;
}
a:hover {
color: red;
opacity: 1;
font-size: 2em;
.transition(e("font-size, color"));
}
And though it seems that LESS accepts that, it will only animate the last property in the comma-separated string you send through. A pity.