Pavonis Interactive Forums

In the original LW, some perk choices granted flat stat bonuses beyond what they displayed. Steadfast conferring +5 will being an example that jumps to my head.

Is there a way to implement a similar system to LW2? Where say I were to give +Aim for choosing certain perks?

Yes, look at Combat Fitness.

The relevant definitions are in XComLW_SoldierSkills.ini

You'd need to add a permanent effect that supplies stat bonuses to the ability itself, so you'd also need to look at how the combat fitness ability template is implemented.