This works to alter the code in the ModifierArguments table (as verified by looking at the contents of the actual game database)
Code:
<GameData>
<ModifierArguments>
<Update>
<Where ModifierId="IDENTITY_NEARBY_GREATWORKS" Name="Amount" />
<Set Value="5"/>
</Update>
</ModifierArguments>
</GameData>
However this does not mean the effect will be seen when loading a saved game. This is because
generally once a modifier has been attached to an Object (and Eleanor of France is an Object in these terms), alterations to the argument data are not implemented. Also, there is no guarantee that Firaxis did not actually code the EffectType used to act as a Boolean, even though an "Amount" argument is being used in the ModifierArguments table.
Nor will the InGame text that is displayed be affected either unless the description tag that explains the effect of the modifier is directly-altered to show the new values. Even if the text tag is altered this does not mean the game is actually implementing the new code effect. Text is just that -- hard-coded text (for the most part) that has actually nothing to do with the thing that is being described. You could change Eleanor of France and Eleanor of England's text to read entirely
Code:
Cheeseburgers! Cheeseburgers! Cheeseburgers! Cheeseburgers for all!
------------------------------------------
If your code looks something like this
Code:
<GameData>
<ModifierArguments>
<Row>
<ModifierId>IDENTITY_NEARBY_GREATWORKS</ModifierId>
<Name>Amount</Name>
<Value>5</Value></Update>
</Row>
</ModifierArguments>
</GameData>
or this
Code:
<GameData>
<ModifierArguments>
<Update>
<ModifierId>IDENTITY_NEARBY_GREATWORKS</ModifierId>
<Name>Amount</Name>
<Value>5</Value></Update>
</Update>
</ModifierArguments>
</GameData>
You have a fatal syntax error in either case which Database.log will be reporting if your XML file is in fact being loaded into the game's database.
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In order to help you fix whatever exactly it is you are doing wrong it is necessary to see exactly what it is you are doing in its entirety.