In terms of have various frequencies open up a guitar, I can't really see how that makes much sense. That can be the case with AMP speakers, and breaking them in, because initially they are stiff and throughout use, the cone "smoothes" out persay. That's why when some people buy new amps, part of what they'll do is just turn it up really loud and strum for a while. It also just happens naturally over time. Some people suggest playing an old radio through the speaker for 24-48 hrs straight to speed up that process.

On an acoustic guitar (and even to extent on electric guitars), what happens is as the woods dry out, the release of the moisture enhances the resonance and response. Tone can be dampened by that moisture. As it ages and you play it, the wood's natural cellular structure changes with the release of the moisture. Now, it's one of those things that's gradual and just attempting to dry out your guitar won't do it.

But, recently higher end builders have begun "torrifying" their top woods before making guitars, which pretty much speeds up that process...

Spruce topped guitars usually have a breaking in period, and over the years become "better." Cedar topped guitars don't really age like spruce.

And, if we're going to get even more detailed... Part of the reason that old Martin's "sound better" is because their bracing pattern is different than it is now. In the past, guitarists used lighter strings, so Martin didn't have to compensate for extra tension on the top wood. As heavier strings came on the market, guitarists turned to them for increased volume, which caused a lot of stress on the tops, so martin had to change the bracing patter. When you see a guitar that says "Pre War," it refers to the bracing pattern.