Inserting columns and keeping everything ?

The attached file is an example. The real workbook is huge, with refrences between almost all sheets. sheet 2 will use some of the totals from sheet1 for instance.

My problem is, this workbook works flawless but has taken about 2 million hours to make.

Now I need a new one, where the days "saturday" and "sunday" are present too - how do I insert those while making sure nothing gets broken?

I've tried inserting a column next to friday, but that messes up something as simple as the =SUM just to the right - it doesnt include the new cell! - wont even begin to think what it does to the refrences in other sheets!

ekstradays1.xlsx

Can you supply a copy of your present workbook in place of the sample that you have given as it doesn't show how the calculations are being made between the worksheets. We need to know this in order to be confident in giving advice.