Technically, the usual approach would be to query the other template and pull out the data items you want/need then apply them to the current composition. So it is not a challenge at all at that level, and I would probably allow the clinician to pull through that ‘suggestion’ based on the admission diagnosis, but of course allow them to override it. But one way or another you are going to have to decide what is the source of truth for the ‘principal diagnosis’. As the system gets more complex, you will potentially have many diagnostic statements made that should never be regarded as being applicable as a ‘principal diagnosis’.
There is nothing to stop you from making the ‘Ward diagnosis’ as the source of truth and linking / referencing that record but I would start with the idea of a separate problem list ‘conttexually’ organised for your kind of scenario (a Community/GP system might well be different).
built by @johnmeredith is an example of the pattern we think might be useful, although this is a hardwired example with inline data not references.