How is the last part of "you might as well be hanged for a sheep as for a lamb" grammatically correct, that is "as for a lamb"?
Don't we use the structure "as for a something" in a sentence like "and as for you" (when it comes to you)?
Are there other examples of this usage - as for a lamb?
The two variants of the adage show different levels of deletion (as does the expanded but rarely met version), all acceptable:
The omission of stealing assumes that the offence is obvious (historical knowledge presumed), while the other deletions are of a more familiar type, omitting repeats of words already given (or retrievable) while not leading to loss of clarity.
I'm familiar with the expression with as a lamb, rather than as for a lamb.
But the as for form is perfectly grammatical. You're right that the phrase as for has a particular meaning of its own, but here we have the accidental sequence of as and for, so it does not have that meaning.
A Google ngram of "sheep as a lamb" vs "sheep as for a lamb" shows the former is always more common than the latter, though between 1980 and 2000 for some reason it was only about twice as common: at most times since 1820 the ratio has been higher.
