I had an existing MySQL table with a few columns, e.g. x, y, and z, and I needed to add a timestamp column `ts` to it. But when I tried, the column was filled with "<Error>" values. Read on to see how I fixed it.
After getting the message, "There is data for this field in the database. The field settings can no longer be changed." while trying to extend the character limit for a text field in a Drupal 7 instance, I used the code below to increase the character limit. It modifies the relevant parts of the database to allow more characters. I ran the SQL code through a content node with the PHP Code Text Filter enabled, but it could also be run in a custom module.