Using local creates a temporary instance of the named variable, and you can do what you like with it.

But this does not apply to all special globals, i.e.:

% perl -e 'local $1 = 1'
Modification of a read-only value attempted at -e line 1.

% perl -e 'local $^S = 1'
Modification of a read-only value attempted at -e line 1.
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-- Frank