You are right, latex paint will not harm the tree. You could always take a small bark chip to HD, and have them color match it. If you want to go crazy, have the color match be a shade lighter, and apply it over the paint. Then get a tube of black paint pigment, and mix it coarsly into a dish of the paint, and apply it with a comb to get a bit of a graining pattern going.
Chemicals certainly do have a risk, as does blasting, as does wire brushing. But it all depends on the tree. If we're talking about an oak with a nice and thick bark, you could brush all day and not cause a problem. If we're talking about a birch, a layer of bark may just peel off and the paint will fall off.
One good point was raised, and that is if you use a brush, you don't have to actually remove the paint. Just break it up, and it will naturally fall off much faster now.
Paint over it with a color that matches the bark. Don't spend much money since the punks will come back.
You're making assumptions. My first thought was the house was being sold after a nasty divorce. That would change everything . . .