{
   no strict 'refs';
   ...
}
# Previous setting resumes after curlies.

##</code><code>##

# Name of the function to wrap.
my $sub_name = '...';

# Symbol table entry of the function we want to wrap.
my $sub_glob = do { no strict 'refs'; \*$sub_name };

# Reference to the function we want to wrap.
my $sub = \&$sub_glob;

# The wrapper.
my $wrapper = sub {
   ...
   $sub->(@_)
   ...
};

# Replace function with its wrapper.
{ no warnings 'redefine'; *$sub_glob = $wrapper; }