I need to replace the xml content(having HTML tag <br /> to be replaced as '\t') after fetching the xml content using the script. Please guide me on this...
I would run a find/replace in Notepad++ (or Mac equivalent), outside of InDesign.
You coulod create an action script that fetches the file, ideally same name/place everytime, replaces what's needed and applies formatting.
You could have an XSLT written to apply to the XML during import into InDesign. I'm pretty sure the XSLT could process the XML to remove the <br/> tag and replace with \t.