Change tile yields with social policies

[Pepijn]

Hey guys,
I am trying to rebalance the social policies and I want to give coast and ocean tiles extra food and maybe other yields when you dive into the exploration tree. I cannot find how to do this does anyone have any ideas? I figured out how to change tile yields but I don't know how to place them into a social policy. This is what I have so far:

<GameData>
    <Policy_TileModifier xxx this probably needs to be something different>
        <Row>
            <PolicyType>POLICY_NAVIGATION_SCHOOL</PolicyType>
            <TerrainType>TERRAIN_COAST</TerrainType>
            <YieldType>YIELD_FOOD</YieldType>
            <Yield>1</Yield>
        </Row>
        <Row>
            <PolicyType>POLICY_NAVIGATION_SCHOOL</PolicyType>
            <TerrainType>TERRAIN_OCEAN</TerrainType>
            <YieldType>YIELD_FOOD</YieldType>
            <Yield>1</Yield>
        </Row>
    </Policy_TileModifier xxx this probably needs to be something different>
    </GameData>

Thanks in advance!