You can add new points as long as you do it in time i.e. having considered their evidence and 14 days before the hearing. The scheduling letter will say 7 days but the Chief Adjudicator's Practice Direction says 14 days for a skeleton argument. However, I firmly believe that the onus is upon the council to file their evidence in good time and then respond to that.
Said PD IMO is inherently unfair -- and I have made my position absolutely clear on this. Example situation: council like Redbridge or Greenwich do not file any evidence at all so you automatically win. BUT, if you file a skeleton argument, this then wakes them up. This is highly prejudicial.