You can change <Weight>22</Weight> for <InternalName>GiveCreditsArtifact</InternalName> in AnomalyDefs.xml to weight of 1 with a mod. This is the anomaly that gives 10% of your current treasury as the reward.
Alternately you can change
SpecialValue>
<Special>PercentOfFactionCredits</Special>
<ValueParam>0.1</ValueParam>
</SpecialValue>
to reduce % of treasury awarded.