OK, having already done this (making Pioneer type traits), if you want to make a 'designable' pioneer, this is all you need:
- <AbilityBonus InternalName="PioneerGearAbility">
- <AbilityBonusOption InternalName="PioneerGear">
- <DisplayName>Pioneer Gear</DisplayName>
- <Description>Allows unit to build towns and outposts</Description>
- <AIData AIPersonality="AI_General">
Save the above code into it's own .xml file in the mods folder, with it's own name (settlers.xml or whatever), and Pioneer Gear will appear as a trait which you can choose, in the same place/row that the Scouting trait appears.
If you wanted to allow outpost building but not town building, simply delete the UnlockAction/BuildTown Game Modifier, which I'm sure you already did. Note that, as an above poster pointed out, you can't design a unit with less than 3 individuals, so keep this in mind when arriving at your values. BTW, my values were something I was experimenting with, choose any resource, training turns, etc. that you feel is appropriate for whatever you are trying to do.
This will, of course, allow your Outpost builders to buy armor and such as well, if you feel the need for armored outpost builders, but I personally don't take an issue with this as the world of Elemental is a dangerous place, and packing some iron to protect yourself is usually a very good idea if you can afford it...
I am (eventually) planning to release this as part of my mini E:LH mod (my roadbuilding trait mod), but of course feel free to use/share this code as you see fit!