How to replace blocks and items in Minecraft .mca files?

Question

Is there a way to turn .mca files into a human readable format? Is there a way to replace all of a certain block or item in a .mca file?
I would like to replace all instances of a modded block with a vanilla block. I plan on updating my Minecraft java modded world into a newer version, but the newer versions of a mod removes some blocks and items.
I would also like to replace items in inventories and storage and biomes too.
I tried opening .mca files in a text editor, but that just gave me a bunch of symbols. Where do I get started? Are those files zipped or something?

Kcats · Answer

One of the most common tools for editing Minecraft files is NBT Explorer.
It doesn't do what you need, but since you mentioned you can program it yourself here are some pointers:
The .mca file format is called Anvil file format and is based on Region file format with changes to the chunk format. The description in the wiki is not very friendly but basically, to read anvil files:

Follow Region file format until you get the chunk blobs.
Once you decompress the blob, it is in Named Binary Tag format which is a generic binary format.
Once you can parse the NBT tags, consult Chunk format to interpret the chunk data.

NBT Explorer is open source, so you'll be able to borrow some code from there, specifically this part seems to be concerned with the actual parsing and interpreting of the data.

aytimothy · Answer

If manually going through NBT Data is not your thing, you can use editors such as:

MCEdit
WorldEdit (Forge Sponge/Bukkit/Spigot)

And mass-editing the world in-game instead. There's also the /fill command.
Edit: This may be what you're looking for

How to replace blocks and items in Minecraft .mca files?

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