Extended ability to alter column type when empty

Hi,

I am a real newbee and I hope this is the right place to post a feature
request.

I am receiving data from a csv file where one column has a strange data
format. It would be nice if I could use Copy From with to_timestamp to
transform the date. As far as I know this is not possible to do in one step
(unlike MySQL I believe). I, therefore, have to first read large amounts of
CSV data into one table where the data is a char(15) column. Then create
another table using:
CREATE TABLE T (like tempT);

ALTER TABLE T ALTER COLUMN thedate TYPE TIMESTAMP;

However, then I run into:
ERROR: column "thedate" cannot be cast to type "pg_catalog.timestamp"

This error comes even though the table is empty. Could it be an idea to
allow this for empty tables? Am I missing something obvious in my
unreasonably complicated approach?

Regards,

David