What if we create separate lists of block IDs for naturally generated blocks and those placed by the player? And configure the behavior using the config. For example, you can configure it so that all blocks placked by the player are not smoothed, but naturally generated ones are smoothed. Or configure separate behavior for different types of blocks (such as natural generatet and as player-placed).
I know that there is a way in the game to check whether a block is naturally generated or placed by a player. This mechanic is used for wooden tools in mods such as Aether and Aether II.

I know that there is a way in the game to check whether a block is naturally generated or placed by a player.

There isn’t really.

This mechanic is used for wooden tools in mods such as Aether and Aether II.

I’ll take a look to see if I can figure out how they do it. Probably they just have a hardcoded list somewhere inside their mod.

This is a great idea in theory but it breaks down quickly when you realise that Sandstone is both a naturally generated (underneath sand in deserts) and man made (desert villages, desert temples) block

I know that there is a way in the game to check whether a block is naturally generated or placed by a player.

There isn’t really.

This mechanic is used for wooden tools in mods such as Aether and Aether II.

I’ll take a look to see if I can figure out how they do it. Probably they just have a hardcoded list somewhere inside their mod.

This is a great idea in theory but it breaks down quickly when you realise that Sandstone is both a naturally generated (underneath sand in deserts) and man made (desert villages, desert temples) block

I know that it is. I used Aether II, it works.
So, need to think about the way to change what kind of block (usual or smoothed) player need to place

Can you please describe the exact mechanic that you’re talking about in Aether II so I can replicate it myself with little prior knowledge of the mod?

Of course. In the Aether II mod there are item that named "Skyroot pickaxe". Every natural generated block (that can be mined by wooden pickaxe) mined by this tool — get double drop

Can you please describe the exact mechanic that you’re talking about in Aether II so I can replicate it myself with little prior knowledge of the mod?