No, that's wrong. The warnings pragma is lexically (statically) scoped, not dynamically scoped.

{
   package OtherModule;
   use warnings;
   sub routine { my $n = 0; my $i = $n + "a"; }
}

{
   no warnings;
   OtherModule->routine();
}
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Argument "a" isn't numeric in addition (+) at 602580.pl line 4.
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And unfortunately, use warnings; (and no warnings;) overrides $^W.

{
   package OtherModule;
   use warnings;
   sub routine { my $n = 0; my $i = $n + "a"; }
}

{
   local $^W = 0;
   OtherModule->routine();
}
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Argument "a" isn't numeric in addition (+) at 602580.pl line 4.
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Update: The warnings was initially a compile-time warning. Fixed it to be a run-time warning.