I have done it too. In my experience, tuners aren't necessarily experienced in voicing because - my guess - few customers ask for it or even know that it can be done (and not all customers have ears sensitive enough so that voicing problems bother them). In addition voicing is very subjective.
The first tuner I hired to do voicing did a lousy and costly job. He went very deep and some hammers still lack brightness at this time (though it has gotten a bit better with my softening the other hammers around).
The next tuner managed to soften the hammers really quickly without going deep using a wide angle needle and I learned from that. He also used a 3 needle tool to "fluff up" the tip of the hammers. After he botched a tuning and unisons went bad after a week, I switched tuner again.
I asked my third tuner (and still current) to brighten and soften some notes and she used chemicals (I have read others RPTs are not too much in favor of chemicals and prefer mechanical means only - needles etc.). It is easier to soften a bright hammer (voice "down"), but it's much harder to voice "up" a hammer that is a bit too quiet.
My Yamaha tends to become brighter after a tuning, so I give a pass or 2 with my wide angle needle, I don't go deep and the effect fades after a few months. I also managed to brighten a few hammers by lightly filing and pounding a bit with a hammer.
If you are reasonably agile with your fingers and follow some precautions like resting the hammers on a voicing block you should be able to do some things on your own. Now if nothing was done for 20 years, it probably needs a lot more than just softening, and this requires expertise to be done right.
I also fixed a bunch of unisons on my own. Yes I read all the warnings and OMG the strings could explode and make me blind and what not. But in the end, I managed to fix these unisons without damage and can enjoy the piano more until the next tuning. I just cannot stand a wobbling unison... ugh.