Is there any work around to update selected columns in a table with the help of CDT and WriteToDataStoreEntity SmartService.

Build your CDT. Your expression should atleast take one input(existing cdt data) and output should be a CDT type. In your expression update the columns for which you want new data and return the updated cdt. Use this cdt in WriteToDataStoreEntity

If you have a case where you're trying to update a very limited subset of the CDT columns and doing this same subset often, you can build a separate CDT with just the column(s) you want to update, as well as the primary key ID which would indicate the row you wish to update. For example you would have a CDT where you pass just ID and STATUS_CODE if you want to simply update the status for that row, etc.

Again, this is if you have a certain subset that you are updating constantly; for one-off cases, vijayana 's suggestion above is probably the most straightforward.