Jelly is definitely a great solution for this… other than it. This would be my solution 
Create a custom component. mixin that component into the existing berry bushes. When that component starts up replace, by some % chance, the regular berry bush with your own.
The main thing that would be different between this and Jelly is that this way you would get great integration of your new berry bush right into the regular berry bush spawns. You’d see regular and Juniper berry bushes side by side. 
This also could be extended then easily to include even more types of bushes, once again all spawning together, instead of separate patches.
All things aside…
The base games offers a great way to spawn things throughout the world. While spawning is part of the problem… making the entity actually harvestable is another issue.
I have a sample which covers all of this
Renewable Resource [r188]
Adds harvestable bee hive, basically a berry bush example, which can be harvested to get edible honey.
Adding recipes to carpenter
Adding entities
Renewable resource example
Food example
Download - https://drive.google.com/file/d/0BynmPA83eY4PWGJTMWtDWWR3RVk/view?usp=sharing
Original Post - Question: How do you add objects to r188?
Basically the issue comes down to the type of spawning you are looking for. The base game can easily spawn things using what have been deemed scenarios. These are used for various things, but in your case, I’d point out the flowers and animals throughout the world are spawned in this way, you could easily adapt a scenario to spawn in your enities.
The scenario technique also leaves room to customize the amount to spawn in, chance to spawn, and what “biome” to spawn in.
Good luck with your mod