When it comes to exporting module, there is a check box which preset to "seal the selected modules". If you don't uncheck that, you won't be able to edit it once imported. (bottom of this document )
On thing you can try is to export the module with that box unchecked and import again to over write existing. Code files many not be included in the export, by default it's only virtual objects, so you will have to manually copy the code files over.