Change the source on a lookup column?

Question

Is it possible to change the data source on a lookup column? I have the source set to list A but I want to change it to List B.

Answer 1

Disclamer: I can not say this is good practice, or very wise, or that it will not break anything.

You can update the SPField Schema XML directly, for example using Client Object Model like this:

var fromList = 'MyList';
var fromField = 'SomeLookupField';
var toListId = '{aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaa}';
var ctx = new SP.ClientContext();
var field = ctx.get_web().get_lists().getByTitle(fromList).get_fields().getByInternalNameOrTitle(fromField);

ctx.load(field);
ctx.executeQueryAsync(function() {
  var schema = field.get_schemaXml();
  schema = schema.replace(/list=\"\S*\"/i, '').replace(/\/\>/, 'List="' + toListId + '" />');

  field.set_schemaXml(schema);
  ctx.executeQueryAsync();
});