I'll like the administrator to be able to:
*Search among already registered members by their Interests,
*Grap these together (with the other metadata) and
*Add them the selected members to a newly registered Group (e.g., a sub-group).

I guess:
it'll need searching & grapping the users ID from metadata and add these to the Groups UI
OR
it'll need to upload a list of well-known members to a Group-ID ( without new registration).

-->It looks like the auto-group membership "autosubscribegroup" plugin as the users are automatically added to a defined group - but it is only active under the first registration.
-->It looks like the "groupsfrommembers" plugin - but it only lets Group-owners INVITE members from the whole community - but it does not let Administrator copy members from one group to another without re-registration. The purpose for my members are to collaborate in the subgroups according to their interests.
-->It lookes like "supergroups" as the users want to create sub-groups - but no addition of registered members
-->It looks like "forms & related plugins" as defined profiles can be found (somhow?) through an advanced search - but the results cannot be handled for e.g. membership to other groups
-->It looks like "westorelggman" in its way to be able to find metadata - but no copy options to 'add' members to other groups... etc.

If reacting - the plugin provider says go elsewhere - as it is difficult and out of their core topic. Please reconsider or help here. I think such plugin fragments are of general interest!

Thanks!