my %subs;
while (<TEXT>) {
   my ($s,$r) = (split qr{/})[1,2];
   $subs{lc($s)} = $r;
}

my $pat = join '|', map quotemeta, keys(%subs);

#$xml =~ s/>[^>]*\b\K($pat)(?=\b[^>]*<)/$subs{lc($1)}/gi;
#$xml =~ s/>[^>]*(?<=\W)\K($pat)(?=\W)(?=[^>]*<)/$subs{lc($1)}/gi;
$xml =~ s/>[^>]*(?<=\W)\K($pat)(?=\W)/$subs{lc($1)}/gi;
[download]

\K requires 5.10, but you could rewrite it without \K. The important bit is to create one pattern.

It assumes you don't have inputs of the form /A/B/, /B/C/

Update: Added required calls to lc.