Daw'r newidiadau hyn i rym am 04:00 ddydd Llun 18 Ionawr tan o leiaf 15 Chwefror, ond maent yn debygol o fod mewn grym am fwy o amser.
These changes will come into effect at 4am on Monday 18 January until at least 15 February, but are likely be in effect for longer.