Changing Identity Seed in SQL Server (Permanently!)

From Books Online:

"To change the original seed value and reseed any existing rows, you must drop the identity column and recreate it specifying the new seed value. When the table contains data, the identity numbers are added to the existing rows with the specified seed and increment values. The order in which the rows are updated is not guaranteed."

MSSQL does not allow you to add or alter an Identity on an existing column via TSQL very easily. You would have to drop the column and re-add it. Needless to say this can play hell with FK relations. You can do it directly in the enterprise manager. However that won't be fun if you have to do this to a LOT of columns.

Is it necessary to create a new column, move the values across, drop the original column and rename the new?

Yup, and don't forget to fix/update all indexes, foreign key relationships, etc. that are tied to that column