One should also keep in mind that this is a game, and not only a game but a mod of a game made by volunteers.
So for everey piece of the lore several checks have to be made:
1) Does the game engine allow this feature? If not, discussion is over. (Seems to be the case here.)
2) Is there anyone in the team who can - and actually will - implement the feature? If not, discussion is over.
3) Is the feature fun to play? Here an extreme example: Imagine Frank Herbert wrote about a master/mastress (perhaps of the Bene Gesserit) who could kill the entire population of a planet (or at least a city) by a simple thought. Sort of a "I win"-button. You wouldn't like that feature in the game although it's part of the lore.
Many games (or mods) failed because of TOO MUCH flavor, disrupting "gameability".
4) Is it really part of the lore? May become a question if different sources show inconsistencies. After all, it's all fiction. But (4) should be the last question in the line.
Thus, the conclusion "Grass: Fremen were planting it on dunes. So in this game grass also should spread to desert tiles" is way too short imho.