I don't think applymap will be required here. If the target date you want to add to both the versions are fixed then you can try something like this.
if(Version='1st half','31/08/2015', if(Version='2nd half','31/12/2015')) as TargetDate
Let me know if this helps.
I'm supposing you want more than simply the year of 2015. Perhaps, you have a spreadsheet with tree columns (Year, Version, TargetDate),
If your original table has the fields Year and Version, you can left join it to the table loaded from the spreadsheet. Any combination of Year/Version not present in the spreadsheet, will result in a null TargetDate. Otherwise, it will contain the appropriate target date
Is this want you need?
Hope this helps you