I usually use XML::XSH2 for XML manipulation. In this case, something like this might work for you:

open 930168.xml ;
register-namespace ce 'http://put-your-namespace-URI-here' ;
for /ce:bib/ce:bib-reference/ce:other-ref/ce:textref {
    my $label = substring-before(.,'),') ;
    if ($label and xsh:matches($label,'\d{4}$')) {
        insert element ce:label prepend ../.. ;
        insert text concat($label, ')') into ../../ce:label[1] ;
    }
}
save :b ;
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I wrapped the XML chunk into ce:bib, your root element might have a different name. Also do not forget to change the namespace URI.