If you do not distribute anything, you are essentially not "copying" stuff. Local copies of content do not fall under copyright law.
Now, in some jurisdications, distributing software that goes out of its way to circumvent copyright protection mechanisms is illegal. This however requires, that the original software, that is to be modified, has security mechanisms that are in place on a technical level to prevent somebody from modifying ("tampering") with the original software.
However, the ASI installer has no such security mechanisms. It has no technical barriers preventing anybody from accessing its files in its original setup. An .MSI is basically just a .ZIP file. In addition to that the author of the the original software must be able to proof, that there are/were concrete damages that the modification causes/caused.
This means that a script that only modifies local files does neither infringe copyright itself nor does it circumvent any barriers that were erected to prevent software from tampering with ASI setup file. And since ASI does not cost money, there are no damages to the original author.
So even in the most restrictive jurisdication thinkable would a local script that installs the ASI files locally be legal.
I am not a layer, but that is my understanding of that matter. By the way, if it it wasn't like this, distributing FAF would be illegal because FAF is modifying FA files, which are of course copyright protected.