Yes, I think both of them work. I tried that before, adding links to old articles or pages and when checked my backlinks through google and other backlink checkers, the backlinks on the old articles/pages appear, so I guess it should work.

I will recommend to put new link with new content Instead of editing the old one.

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It should work, But posting links on old articles? This is not gonna benefit you much and the link PR will now be distributed in more domains.

Instead of editing a very old article you could better write a short and new one. Your link would give better juice in fresh content when compared to an outdated content that has cached long ago!!

I think you are asking does linking out from an old article have any SEO benefit to the page you are linking to?

The answer is a big YES

Your old article is more likely to have generated backlinks, so holds more potential to rank other webpages you link to from the old article.

A good guide is does the old article have any SERPs?

If the SERPs are semi-competitive (you had to work hard on backlinks to gain them) the links from that webpage will probably be worth more than a similar webpage on the same domain with a similar level of internal links.

Never under estimate the SEO power of links from ranked content, if it's ranking you know Google trusts it.

David