Importing lists of members of some federation is often a good OpenRefine exercise.

For instance, the Federation of Museums and Art Galleries of Wales has a public members list. We could use this list to link items about each member to the item about the federation via the member of (P463) property.

The list can be scraped from the federation's site, which results in this table: http://pintoch.ulminfo.fr/aa469ac9f0/welsh-museums-federation-members.tsv

We can then reconcile this to Wikidata in OpenRefine.
Because we expect these organizations to be charities registered in Wales, we can also reconcile them against that charity registry. This is possible thanks to the FindThatCharity website, which offers an OpenRefine reconciliation interface for charities, which can be added with the following URL: https://findthatcharity.uk/reconcile

This can be used to obtain registration numbers for the member organizations, helping us to create better items for them.