My guess: that depends on the firmware in the camera. So it might be different between make and model.
If you have already downloaded them to your PC, it might be possible to do it with a photo editing program, but only if the date that shows on the downloaded picture is taken from the metadata. If it are pixels in the picture, nothing and nobody knows what was hidden behing them.
On a recent vacation, I didn't notice that the date/time stamp was turned on. I have changed the settings on the camer, but how do I remove the date/time stamp on the photos I've already taken?