Is there a way to verify if an NFT based on the Metaplex standard is immutable and cannot be changed by the original creator?
2 Answers
The easiest method if you just want to check manually for a single NFT is looking at an explorer (solscan.io, Explorer.solana.com , solana.fm) and check if it is shown as immutable there.
If you want to check programmatically you should pull the metadata and check the immutable field. This can e.g. be done through the js sdk or also in an on chain program with rust.
Checking the immutable field is enough since every metadata change has to go through the metaplex token metadata program which only allows the update if immutable = false
In addition you should confirm that the uri is hosted in a immutable storage solution like arweave.
You can look up the token address of the nft on Solana Explorer or Solscan and it will show if is mutable 
