Would it be possible to add the ability to use this function to also cut down giant mushrooms, such as in a dark forest or mushroom island.

As this is a hub for all mods, I think you mean for Tree Harvester right?

Thanks for the suggestion! This has been added in version 5.0 of Tree Harvester.

https://www.curseforge.com/minecraft/mc-mods/tree-harvester/files