Hi All,

I have a question.  If someone wanted to overwrite a portion of the Bitcoin blockchain with random data and have it still validate in place of a correct block, would this be computationally difficult/impossible?

The reason I am asking this question is the following:

German Researchers: Child Abuse Content Found On Bitcoin Blockchain, Users Must Be Protected
https://cointelegraph.com/news/german-researchers-child-abuse-content-found-on-bitcoin-blockchain-users-must-be-protected

So the question is, "is it practically possible to overwrite those portions of a bitcoin block that currently contain URLs to apparent CP repositories and still have the block validate properly?"

I know to do this to substitute useful data would be practically impossible.  But if one is looking to destroy existing data by overwriting it with any other random string that would compute the same hash (could be completely random in place of these URLs), does that then make the exercise within reach from a computational perspective?

I am in no way suggesting that this should or should not be done, I just want to get an experts view of the feasibility of doing so.

Best regards,
Ben