RE: Local currency needs to be changed for the historical data
My recommendation to you will simply be not to do this and not even try to do it.
You should create a new NAV company that is configured with the correct currency from the begining.
Then you can discuss with your partner how they can assist you in converting the data you need from your old NAV company to the new NAV company.
And because you are on NAV 2009 you should take the opportunity to upgrade to Business Central at the same time.