(Oops. Didn't really need to dash off, on second thought.) I slightly suspect your example is more complex than I can deal with. What I meant is simply something like this (and I think it does not matter if the values are simple scalars or references to something complex):

%what_all_workers_have = (
                            holidays       => 30,
                            hours_per_week => 40,
                            office_space   => 10,
                            job_title      => "Clerk",
);

## turning to John, who is a wheelchair user:

%what_john_has = (
                   %what_all_workers_have,
                   office_space   => 20,   # needs room to maneuvre
                   hours_per_week => 35,   # needs more breaks
);
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One needn't even worry if %workers_have actually contains the keys office_space and hours_per_week. It will either add or overwrite them, whichever is required. To me, this seems quite elegant and time-saving. In any case, it's less code to type than any other version I could think of.