I use Wood to Landfill and SchallUncraft (https://mods.factorio.com/mod/SchallUncraft). The latter usually returns the resources that went into an item. However, on uncrafting landfills made with Wood to Landfill from my inventory, I got stone instead of wood. Could you provide a proper uncrafting recipe, or would that break everything?

Not the way I currently do it. All I did was add recipes that create the default landfill item already in game. In order to make them uncraftable, i would have to make new landfill item so they would know what to uncraft into. I'm sure that it is possible but it might make the two different types of landfill unable to stack in your inventory. But I havent been playing factorio recently so I'm not going to be working on adding that type of feature to it right now. When I restart I make take a look at it.

Sorry, I somehow missed your reply! It makes sense, same item from different recipes is easier to handle (less work for you, obviously, and allowing to stack differently made landfills for players) then different types of the same item. On the other hand, having just one item may lead to strange results: Normal landfill usually has no fuel value, and neither has yours. However, I also use the Dirty Power mod. With only Dirty Power active, landfill still has no fuel value -- but if I add your mod, both types of landfill have the same fuel value (40.0MJ). While it makes sense that you can burn a heap of wood instead of dumping it into a hole, it's weird that you could burn a load of stone just as easily. Perhaps the fuel value for landfill could be removed altogether in the Dirty Power, but something like this is likely to creep up again, with some other mod.
(EDIT: Meanwhile, the issue with fuel value for landfill has been fixed in Dirty Power.)

I'm not sure what's better: having just another recipe for the same old thing, or having two different items. I'll leave that for you to ponder -- when you're in the mood and have the time for it! In the meantime, I'll just enjoy the means your mod gives me to get rid of plenty of excess wood … :-)

I can see benefits to handling it both ways. Being able to burn wood based landfill makes lots of sense and burning stone based landfill is just fun to imagine. At this point I'm going to leave it as is because I'm not quite ready to come back into this full force. Most likely once my friends and I get tired of Space Engineers I'll be coming back to factorio and I'll take another look into how I want to handle it.