You should only remove the code when you are sure you have finished editing your document.
As well as a requirement for submission, this also allows you to make small edits to your references in Word if required (useful if your output style meant a reference wasn’t displaying as needed). This process is not reversible so make sure you save the version without the field codes as a new document. Keep a copy of your original document with the field codes in case you need to go back and make further edits.
To save a copy of your Word document without Mendeley field codes, click on Export as from within the Mendeley Cite-o-matic tools, and select Without Mendeley Fields.