Yes, you will have to modify every single calculation, form, and report to add the new dimension. As for the data, I know when you do it in Essbase, you are asked to choose a single member of your new dimension to put the data on to. Not sure if Planning does this. However, you could export the data, and create a load rule that has that member in the header.
Thanks Sabrina, so looks like this is the only way then , will try it
Have a good day.