This is an example of how you can use and edit the focaldistmodifier (it is from the files I shared few pages back with all my "messy" research).
Code:
#### Focal distance modfier
<property name="focalDistInitialValue" type="float" value="-10" />
<FocalDistModifierCollection>
<FocalDistModifier>
<FIFAExpressionProperty>
<property name="PropertyName" type="string" value="focalDistEndTime" />
<ExpressionTree.Variable>
<property name="float" type="float" value="1" />
</ExpressionTree.Variable>
</FIFAExpressionProperty>
<property name="focalDistFinalValue" type="float" value="-10" />
</FocalDistModifier>
</FocalDistModifierCollection>
### Zooom modifier might be required
<property name="zoomInitialValue" type="float" value="1.35" />
<ZoomModifierCollection>
<ZoomModifier>
<FIFAExpressionProperty>
<property name="PropertyName" type="string" value="zoomEndTime" />
<ExpressionTree.Variable>
<property name="float" type="float" value="12" />
</ExpressionTree.Variable>
</FIFAExpressionProperty>
<property name="zoomFinalValue" type="float" value="1.8" />
<property name="zoomCurveType" type="int" value="4" />
</ZoomModifier>
</ZoomModifierCollection>
<FocalDistModifierCollection />
But if I may, I don't think focaldistmodifier will be of any help for what you want to do. If I remember correctly, it changed the location where on the picture it looks sharp (vs blurred). It might be useful for replay not sure you can make anything out of it for gameplay.