Is modifying the symbol table to redefine subroutines evil?

tlm has asked for the wisdom of the Perl Monks concerning the following question:

Is this evil:

sub foo {
  call_me_only_once();
  no warnings 'redefine';
  *foo = sub { ... };  # the final foo
  goto &foo;
}
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Update: inserted the missing "no warnings" line.

the lowliest monk