Can chipboard be used to cover with fabric and put in back of bookshelves to give a different look?

Yes. But what is on back of bookshelves now? If you can remove the shelves, glue fabric directly to shelf back, reinstall the shelves and save the extra work and expense. If shelves not removable, cut fabric to fit and do the same thing. I don't see the value of chipboard simply as something to first attach the fabric to.