Test badge: 
This is a simple tool to remap UUIDs in minecraft worlds.
It follows heuristics to find UUIDs in the world files and remap them to new ones.
cargo install --path .See the help message for usage information:
uuid-remapper /path/to/world csv /path/to/player-old-uuid-new-uuid.csv
uuid-remapper /path/to/world json /path/to/player-old-uuid-new-uuid.json
uuid-remapper /path/to/world list-to-online /path/to/player-list.txt # This will use the Mojang API to get the new UUIDs
uuid-remapper /path/to/world list-to-offline /path/to/player-list.txt # This will use the Mojang API to get the old UUIDs
uuid-remapper /path/to/world usercache-to-online /path/to/usercache.json # Same as list-to-online, but uses the usercache file in the server directory
uuid-remapper /path/to/world usercache-to-offline /path/to/usercache.json # Same as list-to-offline, but uses the usercache file in the server directory
uuid-remapper /path/to/world offline-rename-csv /path/to/player-old-name-new-name.csv
uuid-remapper --helpWhen you are asked to confirm the information (Mainly the function used to remap, and the path of the world), you must answer yes (case-insensitive) to proceed. Make sure you have a backup of the world before running the tool.
The main idea is find and replace.
for file in world:
if file is *.txt, *.json, *.json5, *.yml, *.yaml, *.toml:
for each uuid: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx, xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx in file and filename:
uuid = f(uuid)
else if file is *.dat, *.mca, *.mcc:
for each uuid: {zzzUUIDMost: xxxL, zzzUUIDLeast: xxxL}, [I; xx, xx, xx, xx] in uncompressed file:
uuid = f(uuid)
for each string field and filename:
process as text file
As uuid-remapper has finished its job on my server, processing 70 GiB of world files with no significant issues, I consider it stable and mark it as 1.0.0. Update will only be made when someone requests a feature or reports a bug.