So, what's the question exactly?
I know for a fact that the Bonus "tiles" can be linked to a terraforming system such as what i added to X-Worlds' planets, but IIRC the feature(s) themselves aren't moddable.
Unless the OP meant the tiny icons which provides extra % to the PI built there, in which case mostly the values are either hard-coded or anyone can indirectly create some new system for it by editing the xml file patterns to match. Trick is, to balance gameplay consequences as somehow proven by the HUGE bonus given with extremes tiles found in XW.
