I was thinking about this over the week.
What I was doing with my implementations that update meta data was adding an another mint block with the same tokens but different metadata. This is obviously confusing, so having an update block would be fine.
For simplicity and getting the standard out, I think it would also be OK to say that the metadata SHOULD be static unless another ICRC extension is used that adds dynamic metadata.
For example, see ICRC-60 NFT Working Group - Next Steps - ICRC-8, ICRC-56, ICRC-59, ICRC-60
So 2 or 4. 