It's possible, but I don't think it's likely. D-notices are very British things - they're a polite request to the media not to report on specific areas, and carry no legal weight. The assumption is that as long as they are issued in good faith, then the media goes along with them and everyone's happy because the security services don't have to start lobbying for censorship powers.
Now, along comes a situation which looks a lot like an attempt at journalistic suppression by the state. The incentive for the media to go along with any potential D-notice has evaporated because this is just censorship by other means, and if you're going to censor us anyway, why bother with D-notices? Issuing a D-notice over harrassing a journalist (via their family, in this case) would be something of a bodyliner, and I don't think even the British press would have a hard time figuring out what to do about it.
Now, along comes a situation which looks a lot like an attempt at journalistic suppression by the state. The incentive for the media to go along with any potential D-notice has evaporated because this is just censorship by other means, and if you're going to censor us anyway, why bother with D-notices? Issuing a D-notice over harrassing a journalist (via their family, in this case) would be something of a bodyliner, and I don't think even the British press would have a hard time figuring out what to do about it.