I don't know if it's better or not but I would try to incorporate the capturing parentheses in the generated pattern rather than having to remember to put them in the substitution later.

my $search = do
   {
       local $" = q{|};
       qr{\b(@{ [ keys %repl ] })\b};
   };
[download]

It just seems safer to keep everything together.

Cheers,

JohnGG