I understand what you're trying to do, but you just can't... not like that. Sometimes however, it's helpful to use a hash slice:

my %hash = ( this => 1, that => 2 );
@hash{ qw/ those these / } = ( 3, 4 );
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The list of keys can be anything that resolves to a list, including an array or a subroutine call so long as it's properly disambiguated so as not to look like a bareword key.

If the object is to add a whole bunch of new elements at once, that's where slices can be quite helpful.