https://forums.adobe.com/thread/2551002

addParagraf

    function addTextToPara(pStyleName, prefixText)  
    {  
           app.findGrepPreferences.appliedParagraphStyle = pStyleName  
           var paraList = app.activeDocument.findGrep()  
           for(var i = 0 ; i < paraList.length; i++)  
           {  
                paraList[i].contents = prefixText + paraList[i].contents  
           }  
           app.findGrepPreferences = NothingEnum.nothing;  
    }  
      
    //Change the argument with the name of the paragraph style you want to search and the text you want to add before that para  
    addTextToPara("Paragraph Style 2", "<1>")