Now ditch the exclamation point so you don't have to say "Yahoo!s."
Copywriting rule number one: If you have to use an exclamation point, you need to reword the sentence.
"He's fast, strong and can jump!" vs "Faster than a speeding bullet, more powerful than a locomotive, able to leap tall buildings in a single bound."
For example almost everyone agrees that single letters are pluralized with an apostrophe. It is somewhat less common to prescribe an apostrophe in the case of a number either. When this is not allowed, an exception is sometimes made for pluralizing the number zero so that it is not mistaken for the letter O.
It is fairly common to pluralize period-less abbreviations with apostrophes. The New York Times, for example, follows that standard. It is more common still for abbreviations with periods to take an apostrophe.
So basically, no. You don't get to just say "this is the rule for apostrophes in all cases" because that's not how the written word works. We (or the publication we are writing for) can choose our own editorial style, and screw anyone who doesn't like it (although you should be consistent, of course).
But interestingly enough, this is one situation where there can be a universally correct answer: a trademark. If Yahoo! puts out guidelines for how they would like their trademark pluralized, and they say it should be "Yahoo!s", then that is what everyone should use. If they say it should be "Yahoo!'s", then that's what everyone should use, even if it violates their usual rules.
The New York Times doesn't do a great job of following that standard if indeed they try to. Searching for CDs gives me many more examples of "CDs" than "CD's" -- the only one I saw was a blog post, which is probably copy-edited less strictly than an article in the paper. Similarly, searching for ATMs gives "ATMs" and "A.T.M.'s", but not "ATM's". Others I found: both "GTOs" and "GTO's", "LCDs", "TVs", both "B&Bs" and "B&B's". The phrase "A's and B's", referring to grades, was always written with apostrophes, as was the phrase "P's and Q's".
One of the fun thing of doing these searches is that really old articles are mixed in with the results. Searching for LPs shows that it has been written "LPs" since at least 1955 and also yields this intriguing headline: "DIGITAL COMPACT DISKS - REPLACEMENT FOR LPs?" from 1983.
But, as a grocer would say, tomatoe’s, tomatoe’s.
She said "Yahoo!" They all gave some "Yahoos!"
Just so long as they don't vacillate as Panic(!) at the disco has.