R – How to use the same field type in multiple lists on SharePoint

Try this:

1. Create a new Calculated column
2. In the Forumla box, enter something like this: =TEXT([existing date column]+30,"yyyy-mm-dd") You can use any date format string you like instead of "yyyy-mm-dd"
3. Make the data type "Date and Time"
4. Make the date and time format "Date Only"

You have several options both of which are going to require further research on your part they are:

1. Use the SharePoint object model (Microsoft.Sharepoint.dll), you must be on a PC within the SharePoint farm.
2. Use the SharePoint web services which can be found at SiteURL/_vti_bin/ you might want to start with Lists.asmx and work from there.

You are going to need some further research as I have said, but remember GIYF.