#target Indesign
var myDoc = app.activeDocument;
var textFrames = myDoc.textFrames;
for (i = 0; i <= textFrames.length-1; i++) {
        if (textFrames[i].overflows) {
            for (k = 0; k <= textFrames[i].paragraphs.length; k++) {
                if (textFrames[i].parentStory.paragraphs[k].appliedParagraphStyle.name == "par1") {
                    textFrames[i].parentStory.paragraphs[k].appliedParagraphStyle = myDoc.paragraphStyles.item("par2")
               }
           }
        }
    }