It will depend a lot on hardware and/or software but I'd bet users would see some artefacting, ghosting, and general noise when they play your x265 file
As another comment pointed out, an encode of an encode is banned on a lot of trackers... Or at least an encode of an already pretty lossy encode (x264) won't be allowed
Does the filesize change much?
Most. Water, for example, takes up more volume in spaces when frozen