Many European countries have this notion of moral rights of an author that persist even if she sells the copyright, including the right not to have their work altered. The problem here is the estate who represent the author after death are doing the altering, in defiance of Dahl’s explicit wishes when he was still alive. Authors should definitely put clauses in their wills to prevent this in the future and possibly legislation passed to make this the default.
I think framing this in terms of the author is the wrong way. Dahl doesn't care that his wishes are not being respected, because he's dead. It's society at large that is being damaged by these changes. Really, rewriting old copyright works while removing access to the old versions (wether approved by the original author or not) goes against the copryight deal: to incentivize creation by granting a limited time monopoly. If that monopoly is used to remove a work or version of it then that's a break of that contract and we should legally recognize such breaches by removing absolving the other side of the monopoly. Remember that once shared, creative works are not the property of the author alone but of everyone.
