MercenaryTiersDefs.xml this gives you all of them 

?xml version="1.0" encoding="utf-8" standalone="yes" ?>

<MercenaryTierList

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:noNamespaceSchemaLocation="../Schema/MercenaryTierDefs.xsd">

<MercenaryTier>

<InternalName>MercenaryTier1</InternalName>

<DisplayName>Tier 1</DisplayName>

<Description></Description>

<Order>1</Order>

<Amount>30</Amount>

<Color>MercenaryTiers1</Color>

    <CannotAffordColor>MercenaryTiersCannotAfford1</CannotAffordColor>

    <Prerequ>

      <TechAge>

        <Option>AgeOfExpansion</Option>

      </TechAge>

    </Prerequ>

    <Material1>Mercinary_Material_01</Material1>

    <Material2>Mercinary_Material_02</Material2>

    <Surface1>GC3_Default_Surface_01</Surface1>

    <Surface2>OverlayTexture_CrossHatch</Surface2>

    <Appearance>GC3_Mercinary_Appearance_A</Appearance>

  </MercenaryTier>

<MercenaryTier>

<InternalName>MercenaryTier2</InternalName>

<DisplayName>Tier 2</DisplayName>

<Description></Description>

<Order>2</Order>

<Amount>30</Amount>

<Color>MercenaryTiers2</Color>

    <CannotAffordColor>MercenaryTiersCannotAfford2</CannotAffordColor>

    <Prerequ>

      <TechAge>

        <Option>AgeOfWar</Option>

      </TechAge>

    </Prerequ>

    <Material1>Mercinary_Material_01</Material1>

    <Material2>Mercinary_Material_02</Material2>

    <Surface1>GC3_Default_Surface_01</Surface1>

    <Surface2>OverlayTexture_CrossHatch</Surface2>

    <Appearance>GC3_Mercinary_Appearance_B</Appearance>

</MercenaryTier>

  <MercenaryTier>

<InternalName>MercenaryTier3</InternalName>

<DisplayName>Tier 3</DisplayName>

<Description></Description>

<Order>3</Order>

<Amount>30</Amount>

<Color>MercenaryTiers3</Color>

<CannotAffordColor>MercenaryTiersCannotAfford3</CannotAffordColor>

    <Prerequ>

      <TechAge>

        <Option>AgeOfAscension</Option>

      </TechAge>

    </Prerequ>

    <Material1>Mercinary_Material_01</Material1>

    <Material2>Mercinary_Material_02</Material2>

    <Surface1>GC3_Default_Surface_01</Surface1>

    <Surface2>OverlayTexture_CrossHatch</Surface2>

    <Appearance>GC3_Mercinary_Appearance_C</Appearance>

  </MercenaryTier>

  <MercenaryTier>

    <InternalName>GovernmentTier</InternalName>

    <DisplayName>Government</DisplayName>

    <Prerequ>

      <Tag>

        <Option>Government</Option>

      </Tag>

    </Prerequ>

    <Material1>GC3_Red_Death_Material_01</Material1>

    <Material2>GC3_Ship_Material_Iridium</Material2>

    <Surface1>GC3_Default_Surface_20</Surface1>

    <Surface2>GC3_Default_Surface_16</Surface2>

    <Appearance>Government_Ship_Appearance</Appearance>

  </MercenaryTier>

    <MercenaryTier>

    <InternalName>JeffTier</InternalName>

    <DisplayName>Jeff</DisplayName>

    <Material1>GC3_Ship_Material_Painted_Metal</Material1>

    <Material2>GC3_Ship_Material_Brushed_Metal</Material2>

    <Surface1>GC3_Default_Surface_11</Surface1>

    <Surface2>OverlayTexture_CrossHatch</Surface2>

    <Appearance>GC3_Mowlings_Appearance</Appearance>

    </MercenaryTier>

</MercenaryTierList>

You need to create a new file in the mod folder, editing the original files in the Steam folder does not work. For example in my folder structure it is in the following:

Documents\My Games\GC3Crusade\Mods\MyMods\Game

The files in the mod folder have the same name as the originals, in your case MercenaryTiersDefs.xml. Just copy and paste the file above into a notepad file called MercenaryTiersDefs.xml and pout into your mod folder as indicated in my post. That should do the trick, works fine for me.