Thanks you for the replies, gents. I guess that goes into the “things I wish I knew then that I know now” category 
When I started with RM only a couple of years ago, “sharing” seemed to be an obvious solution to a Residence Fact when the people in each household change every 10 years and the Head of the household (more or less) remains the same. It was a quick way of attributing notes, sources and media to the other household members and these shared events appear in the person’s timeline
I’ve found other discussion topics about whether to use Residence or Residence (family) facts for census data but I understand Residence (family) only adds the spouse (a bit like Marriage) but not the children. Jerry also explains the “philosophy” behind family facts here [Census and Residence (family) - How do you add more than just the spouse? - #4 by thejerrybryan] which I do, sort of, get.
I’ve got literally hundreds (possibly more) of shared census facts and I’d hate to have to retrospectively change them all individually. If I were to change the fact type from Residence to Residence (family) would that automatically add the spouse to the head of the household even if it does not add the children? It would be a little victory at least. Secondly, is it even possible to do? I know one can change the fact type for an individual, but globally?
Many thanks again!
Edited to add: I’ve just tried changing the fact type for a married individual and his children - when selecting the new fact type Residence (family) (or even Census (family) come to that) does not even appear!