Are you talking about some way to e.g. break up Arabic into isolated forms? My cursory reading on the matter causes me to guess that this is what you're trying do to. I can think of a few ways to do that, but if my guess is incorrect, I'd rather not waste your time (or mine!) with my suggestions. The rlig OT feature isn't something you're supposed to be able to turn off at all, is my understanding. If you needed to decompose glyphs, you'd need to use a different tool. (I'm imagining it'd be something like a font editor, not a page layout app, for what it's worth.)
If what you want is to decompose Arabic into isolate forms within InDesign, I actually think that a GREP query where you replace each character by itself, followed by a ZWNJ, might get you a string of Arabic isolate forms. But is that actually going to help you? I have no idea whatsoever. Can you give us a bit more detail?