I am only guessing, but in extreme cases it may be perceived as criminal because it is property damage. I emphasis the word extreme.
In practice, I think the probabilty that a property damage charge would ever be taken is negligent. But then, some people don't need to have a lot to complain about, to make a complaint. As a crimininal case, I imagine the reverse graffiti would want to be extraordinary before An Gardai would take it seriously.
But of course, just because a law is not enforceable its intent can be clear. Graffiti is graffiti. The city of Rome is a disgrace altogether with graffiti. That said, I love to see murals.