It's probably best to use an appropriate module for this. Net::LDAP::LDIF appears to normalize the entries. I haven't used perl-ldap much myself but as far as I know it's a very good module for LDAP.

use warnings;
use strict;
use Net::LDAP::LDIF;

my $ldif = Net::LDAP::LDIF->new("test.ldif", "r", onerror=>'die');
while ( not $ldif->eof ) {
    my $entry = $ldif->read_entry;
    print $entry->ldif;
}
$ldif->done;
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Given the following input, the last three lines before the dash are transformed into one line "foo: BarTest123Blah", which I guess is what you want?

dn: cn=Test,ou=Foo,o=Bar,c=US
changetype: modify
replace: foo
foo: Bar
 Test123
 Blah
-
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