Two nameserver questions

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http://serverfault.com – In Godaddy's Zone File Editor, I can edit A/CNAME etc. including NS record. I am wondering if I change NS to another Nameserver, will my records, like A/CNAME, be deleted right away? If I have more than two dns records, and they are mixed by different DNS servers, for example, ns1.abc.com ns2.abc.com ns1.efg.com ns2.efg.com will that cause any issue? Thanks! (HowTos)