We have a nonclustered index that we want to add another INCLUDE column to. The index is frequently being used and also frequently getting INSERTs, UPDATEs and DELETEs. We recently tried dropping the index and recreating it, but we encountered blocking problems (looooong blocking problems). The DROP INDEX was being blocked by other processes. So we're a bit wary of that approach now. What is the best way to manage these sorts of changes to a busy index?
What's your version of SQL Server? If you have Enterprise edition, you could do CREATE INDEX WITH DROP EXISTING, specifying ONLINE=ON. Otherwise I think you should try finding a window of time when there's least activity on the table. If you have activity 24/7 and run on a Standard Edition license, you should consider switching to Enterprise.