This is a good point. We can release a version without the new terraforming resources, but we'll think about a better way for existing savegames.

Maybe a building type which makes the conversion by consuming old resources and making the new ones?

Did the latest update fix this for you?
You now have a building to produce each material. On non-mod saves you'll have to colonise more world's since the resources won't appear naturally in your galaxy.

Yeah it works, unfortunately the saved game now crashes every month because of the general instability of Stellaris right now so I'm going to have to start a new game anyway. Thanks for being receptive and trying though

No problem. You might find the cause of the crashing in your error files: C:\Users\YOUR USER HERE\Documents\Paradox Interactive\Stellaris\logs\error.log