HC
Check boxes may have some value after all, inspired by your request. I made this.
<$wikify name=tagvalue text="<<now YYYY/0MM/0DD>>" >
<$checkbox field=item-review checked=<<tagvalue>> unchecked="" >
Reviewed today
</$checkbox>
</$wikify>
In your tag example when tomorrow comes the checkbox should be empty with yesterdays tag still on the tiddler. Using the Check Box will add another tag on the tiddler.
In my example tomorrow the check box will be unchecked, but checking it will replace the value in field=item-review
<$wikify name=tagvalue text="<<now YYYY0MM0DD>>" >
<$checkbox field=reviewed-day checked=<<tagvalue>> unchecked="" >
Reviewed today
</$checkbox>
</$wikify>
This has led me to make Day/Month Year reviews
<$wikify name=tagvalue text="<<now YYYY0MM>>" >
<$checkbox field=reviewed-month checked=<<tagvalue>> unchecked="" >
Reviewed this month
</$checkbox>
</$wikify>
Of course a lot more is possible.
Regards
Tony