Rome.lnt lives in data/menu folder, you can put a different version in your mod-folder/data/menu to just effect that which is handy.

Modding it is a little difficult you first need to identify which page you are looking for.

pages start
<lpage>
and end </lpage>

you should find a page
<lpage>cb_customize_army

which ought to be the custom battle one....

under that you'll find chunks like:
Code:
    <UI piece>ca_experience_template
      <identifier>UIP_ARMY_EXP_INDICATOR</identifier>
      <Parameters>
        <x>186</x>
        <y>436</y>
        <width>28</width>
        <height>38</height>
        <tool_tip_id>UI_CUSTOM_EXPERIENCE_TOOLTIP</tool_tip_id>
      </Parameters>
      <object_id>ca_experience_template</object_id>
    </UI piece>
    <UI piece>arrow_large_left_discipline
      <identifier>UIP_ARMY_EXP_DECREMENT</identifier>
      <Parameters>
        <x>154</x>
        <y>439</y>
        <width>14</width>
        <height>30</height>
        <tool_tip_id>UI_CUSTOM_EXPERIENCE_TOOLTIP</tool_tip_id>
      </Parameters>
      <object_id>arrow_large_left</object_id>
    </UI piece>
and
Code:
    <UI piece>arrow_large_right_discipline
      <identifier>UIP_ARMY_EXP_INCREMENT</identifier>
      <Parameters>
        <x>229</x>
        <y>439</y>
        <width>14</width>
        <height>30</height>
        <tool_tip_id>UI_CUSTOM_EXPERIENCE_TOOLTIP</tool_tip_id>
      </Parameters>
      <object_id>arrow_large_right</object_id>
    </UI piece>
which I'd suspect are the relevant bits - but it is a bit of a nasty file! Make a back up version of it and try deleting sections making sure you go from
<UI piece> to </UI piece>
and see if you can locate the relevant bits.