edit file: /opt/couchbase/lib/ns_server/erlang/lib/ns_server/priv/public/js/documents.js
(from 4.5.0 : /opt/couchbase/lib/ns_server/erlang/lib/ns_server/priv/public/ui/app/constants/constants.js)

var DocumentsSection = {
  docsLimit: 1000,
  docBytesLimit: 2500, <-- modify this value to edit bigger document

Pour la version 4.5.0 (see https://stackoverflow.com/questions/39465288/warning-editing-of-document-with-size-more-than-256-kib-is-not-allowed)