As Civinator says, you can use extra free techs to specific civs that you can label as a "new" trait, which can also provide buildings. However, to display this in the civ screen you have to either rename the default traits via the labels.txt or just include it in the civilopedia (only the original hard-coded traits are displayed in the civ description box). If you rename an existing trait, that civ also gets the original benefits along with whatever you have chosen as extra. There is no ingame tracking whether a benefit is from a trait or not. So if you say so, and all the indicators ie, a specific set of civs have access to it, then who is to say the trait doesnt provide such a bonus?