writeXml in PresetEffects.xml of After Effects

Hi, i want to make a script to add lines in the PresetEffects.xml file inside After Effects/Content/Resources detecting if is Windows use C:/Programs/etc.... or if is MacOs   Applications/etc...  

and add this lines at the end but before the last line </Effects>:

<Effect matchname="OpenTag1" name="$$$/AE/Preset/OpenTag1=OpenTag1">

  <Popup name="$$$/AE/Preset/Txt=Txt" popup_string="$$$/AE/Preset/Txt/Popup=Texto libre|-|Hoy|Manana|-|Este lunes|Este martes|Este miercoles|Este jueves|Este viernes|Este sabado|Este domingo|-|Esta tarde|Esta noche" default="1"/>

  <Popup name="$$$/AE/Preset/ColorSystem=Color System" popup_string="$$$/AE/Preset/ColorSystem/Popup=Amarillo|Morado|Light Blue|Mid Blue|Dark Blue|Rojo" default="1"/>

  <Popup name="$$$/AE/Preset/Ctn=Ctn" popup_string="$$$/AE/Preset/Ctn/Popup=Short|Mid|Long" default="1"/>

</Effect>