Trading gold % with other AI

[Optik]

We can update trade gold in general, by updating the Trades.xml, like a game rule.

<Trades>
<Row>
<ID>0</ID>
<Type>TRADE_GOLD</Type>
<Description>TXT_KEY_GOLD</Description>
<InitialPercent>100</InitialPercent>
<AIWeightPercent>100</AIWeightPercent>
</Row>

But is it possible to increase it for an unique Civilization?
Because if I update as GameRules, all other civilization could benefit from this improvement. It could be a great unique attribut for a Leader.