You can edit the attribute values of multiple selected features on the Quick Info or Feature Info palette.
For attributes that vary across the set of selected features, the value is shown as "Varies".
You can also use the drop-down list at the top of the palette to select groups of features by type.
To select a series of features, click the first feature and while holding the SHIFT key, select the last feature in the series.
Note: You can also copy an attribute's value and paste it to a selection of other features. The features can be of differing types.