I was trying to do something similar recently. I tried several different approaches and received some guidance from jmcnamara. In the end, I went with the following because I already has most of the code in place.

I simply read the spreadsheet line by line and write it to a new one formatting as I go. (I tried to read the formats and apply them to the data but it wasn't working as expected so I will need to further investigate that.)

If I were starting fresh, I would use the Spreadsheet::ParseExcel::SaveParser module like jmcnamara recommends.

As far as the formulas go, you already know what they are, so it should be a piece of cake to put them back in the right places.