Quick solution to adding the Roadbuilding ability to a specific faction's pioneers without actually modding would be to edit 2 xml files directly and will only take a few seconds. I will use the Alatrian Race for example, but you can use this trick for any of the races (Naturally it will require the proper race name).
First edit the CoreUnit XML file:
1. Locate the string for Unit_Pioneer_Altarian (or the race you want to edit)
2. Replace this string:
<SelectedAbilityBonusOption>Blood_Altarian</SelectedAbilityBonusOption>
<SelectedAbilityBonusOption>Weak</SelectedAbilityBonusOption>
with this string:
<SelectedAbilityBonusOption>Blood_Altarian</SelectedAbilityBonusOption>
<SelectedAbilityBonusOption>RoadBuilding</SelectedAbilityBonusOption>
<SelectedAbilityBonusOption>Weak</SelectedAbilityBonusOption>
Next you edit the CoreAbilities XML file:
1. Locate the string for RoadBuildingAbility
2. Change this variable
<Attribute>Race_Type_Mancers</Attribute>
to this:
<Attribute>Race_Type_Altarians</Attribute> (or the race you choose to add this ability to)
Hope this helps.