Adding a leading zero to a column of data

[Semper.Fi.Rob]

My organization recently changed its number system for our case files from four digits to five digits. The former included a four digit case number, followed by a dash, followed by the four digit year, then another dash, and finally the three digit office identifier (ie: 0100-2014-035). The attached spreadshet contains a sample of historical data I must maintain for a rolling 5 fiscal years. Can anyone describe to me a formula where I can simply add a leading sero to our case number?

Thank you!

[protonLeah]

Insert a helper column adjacent to the case number column and use:
="0"&A2, copied down. Select the new format column then copy/paste special over the old column, delete the helper.