Change the style for plots to dashed curves:

Restore the system default:

Reset the default precision for HilbertMatrix:

Now HilbertMatrix uses machine numbers by default:

A specific option setting overrides the new default:

Restore the system default:

Start writing to a temporary file:

Set the page width to 10 characters:

Write Range[10] to the file and close the stream:

Line breaks occur at the 10th column:

Create a reference to the input cell:

Change the background of the cell to red:

Restore the setting of the cell, which will cause it to inherit from the notebook:

Change the Permissions of a CloudObject:

SetOptions can be used to modify protected symbols:

The option has been modified:

The symbol still has attribute Protected:

Restore the system default:

SetOptions resets the Permissions value entirely (except for the owner's permissions):

SetPermissions only resets the capabilities of the given user groups:

SetOptions can only be used to change the default value of an option, not to add a new one:

Use AppendTo, PrependTo and similar functions to add additional options to a function:

For notebook options with rules, it can be awkward to make a targeted change to a specific rule:

CurrentValue provides a better way of adding or changing specific rules: