Mp3tag list view is basically a somewhat "passive output" view to the tag fields and their inner data, although it is possible to use scripting language expressions to modify tag field data for visual presentation.
What you have tried, this can work, anyway, but you have to save each track manually by pressing [Ctrl+S] or by moving the current list pointer up and down or such other navigating (related option must be set to do so).
As you have mentioned - this is one possible way to make manually changes to the content of tag fields - but there might be other ways to go in Mp3tag how to manipulate values in tag fields.
For mass editing you can use an action or a group of actions, right configured to your need - there lies the power of Mp3tag.
Taking your example from above, you can solve this task using an action "Format value" and a liitle bit of Mp3tag scripting language.
Action: "Format value"
Format string: $if2(%YEAR%,'2010')
Run this action against the selected files ... that's all.
If you need an automatically "running" fix value for each current year ...
Format string: $if2(%YEAR%,$left(%_date%,4))
Format string: $if2(%YEAR%,$left(%_datetime%,4))
This scripting expression might depend on the local computer DateTime setting.
If your computer has a DateTime setting accordingly to ISO 8601, then it should work.