Convert use charnames into BEGIN { ...; require charnames; ... } to be able to use %hash as the value for :alias export tag ...

# cat custom-name.pl; perl custom-name.pl

use strict;
use warnings;
use Data::Dump qw[dump];

BEGIN
{
   my $char = ord( q[a] );
   my %hash = map { $_ => $char++ } qw[ aey bee ];
   print dump( %hash ), qq[\n];

   use v5.16;
   require charnames or die $@;
   charnames->import( q[:alias] => { %hash, q[cea] => $char } );
}

printf qq[aey: %s\ncea: %s\n],
   qq[\N{aey}],
   qq[\N{cea}]
   ;
("bee", 98, "aey", 97)
aey: a
cea: c
[download]

... thanks to the response at https://stackoverflow.com/a/63018246, found via search for "perl begin use require export" as the documentation for use & require was inadequate.

Later I checked again & found use -- what I was really looking for (and realized MetaCPAN makes for a bad search engine for perl non-module documentation)!