How could communication with the past be used responsibly?
Rules of writing a good message to send to the past
Let us assume that the prophecies Nostradamus received were indeed messages from future scientists and that all true prophecy is created with help of future time travel technology. What could we then say about the contents of those messages.
Before using the science in a responsible way, scientists are likely to test their theories and confirm that time travel and communicating with the past is possible. logicaly any experiment needs to be carefully planned and conducted in order not to cause any collateral damage. Future scientists will definitely be concerned with the possibility that communicating with the past might lead to changing their own history time line with obvious consequences. Changing the past is undesirable.
Any messages with prophetic content need to be carefully planned, constructed and coded in order to avoid 'hacking' by the receiver or its contemporaries before the events take place.
Since Scientists probably presume that the future of the receiver is their own past, it will be in their interest that nothing get changed. Even relative small changes in history might have huge consequences over time.
Since the sender cannot know the consequences and impact of sending messages until after receipt, it will be impossible to tell what might happen. From this perspective, not only the content of the message but also the pure existence of a work of true prophecy could start a tragic chain of events.
One of the core issues with communication in general is that you don't know whether you got through to the other side until you receive confirmation. One-way communication is even more tricky as it needs another channel for the reply. Without confirmation you never know whether your message has been received.
Since scientists might want to have a 'confirmation of receipt', they probably want to motivate the receiver (prophet, seer, medium) to record the message.
How would future scientists proof that you can send messages to the past? How would a prophet reckognize a message as being genuine. Would he realize where it comes from and what he is supposed to do with it? And how would scientists prove that a prophet's work of ancient times is in fact the confirmation of receipt of their message?
Since a message is the only way of communication it should contain all the information needed, it should therefore be constructed very carefully and include instructions for writing the seers manuscript: a confirmation of receipt.
In conclusion: what are the rules messages must keep to in order to qualify? There are two parts that must qualify: a part relating to the vision and a instructive part on how the receiving prophet should construct and write his manuscript.