[Koha] [koha] Collecting Dewey codes ?

Hello, I want to collect dewey codes to complete my database. I was thinking about using z39.50 servers to get them but I have 2questions: - I want to use 2 different servers; one in marc21 and one in unimarc. As z39.50 only works for servers using the same format as me, Is there a way to collect the dewey code of the other server with an alternative? What about SRU ? - My second question is: When importing that dewey code, I dont want other data (like title author etc) to overwrite mines. How can I do that? Thx for responses, Frederic Edmont