So I did try it and here's the response I got back from them today. "Thank you for letting us know, this however will not affect the eCOPR and does not need to be changed or reissued."
As I suspected, the date of entry error was not worth fixing. If it were a more significant error (e.g. name being misspelt), I don't know what they would have done - i.e. would they have fixed it or would they have asked me to courier documents to Ottawa (as has been the case for others). But I think it's worth a shot to email them and get some guidance