Flying through known or forecast icing

Tain't legal. The simple answer.

The more important question is: Can you figure out a way to do it
safely
so you don't draw attention to yourself?

For example... you never punch up thru a layer unless you have pilot
reports about
tops or you stay over a place that has wx good enough to get back with
100% certaintly if things go badly as you try to get on top.

As you go along, you must be sure you always have a 100% out. If it's
less than a 100%, you might get in a bad situation.

So you can operate not legally but with safety if you can figure this
out.
If you can't play out the whole solution, or don't have a continuously
updated 100% out, it's a no go.

On top is the answer in little airplanes. You don't start down until
you can get cleared the whole way down. You need good deals with
ATC to get this. Never descend thru a layer unless you have
reported weather underneath and are absolutely sure you can make
the approach. Search on N100KC for a dreadful example of violating
this idea.

The guys who claim they will never do this actually will when the
chips are down! So best is to think the problem through in great
detail rather than assume you will never do it.

Just one more thing: Always understand the wx well enough to
recognize the chance for freezing rain. It will bring you down! Night
time
makes this all much worse!

Bill Hale