sqlite3 change column default value

I don't think you can without replacing the whole table. From the fine manual:

SQL Features That SQLite Does Not Implement

Complete ALTER TABLE support
Only the RENAME TABLE and ADD COLUMN variants of the ALTER TABLE command are supported. Other kinds of ALTER TABLE operations such as DROP COLUMN, ALTER COLUMN, ADD CONSTRAINT, and so forth are omitted.

So there is no way to modify an existing column in SQLite. I think you'll have to create a new table with the appropriate default for hidden, copy all the data over, drop the original notes table, and then rename the new one.

SQLite stays lean by purposefully omitting a lot of features.