Where should I add "ing" in the short form? [duplicate]

If you're using a non-verb acronym or initialism as a verb, you're already in the realm of jargon. If you're writing in a context where that's acceptable, you should add a simple "ed" or "ing" for a suffix unless you're going for a humorous effect. When acronyms are absorbed into the language, they may acquire verb forms; for example, the verb meaning "to produce a laser beam" is "lase," retroactively treating the acronym for "light amplification by stimulated emission of radiation" as if it meant "something that 'lases.'"

I think it depends on context, in my case I use an apostrophe as needed.

• SMSed looks fine to me.

• MACing, however, sounds like we're using a mace (weapon/spray) on someone. For such case I would go with MAC'ing¹ which makes the intent clearer.

¹ MAC is Message Authentication Code

_{^{P.S. I'm not from the realm of languages, but wanted to add some additional info on what I do in practice.}}