There really needs to be an option to turn off all type conversion globally for all files in Excel.
Its not a perfect solution, but its a passable work-around.
The real problem arises when you ask someone to send you data in CSV format. If, in between exporting it from their database and sending it to you, they happened to open and save it in Excel, you will get corrupted data. Usually the sender is blissfully unaware of what Excel's automatic type conversion does to their data.
CSV has been made unreliable as a format for data exchange between companies (aka EDI) largely because Microsoft decided that CSV files should always be opened in Excel by default in Windows. At the very least they should turn automatic type conversion off for CSVs.
The official way to do it is to insert a single quote at the beginning of every field that you don't want auto-converted. In practice this is a time-wasting pain in the neck and ruins your data for use outside of Excel.
But yes we'll probably stick a letter in there.
If you're changing SKUs anyways you may want to change it to have a letter to that Excel "guesses" correctly by default.