There are four cards affected, but it's really only one change. Seriously.
Four older cards referred to a creature or a creature card "with morph." Megamorph is a variant of the morph ability, so these four cards should respect that. So "morph" becomes "a morph ability" on Backslide, Dermoplasm, Master of the Veil, and Weaver of Lies. For example:
Turn target creature with morph face down.
Cycling U (U, Discard this card: Draw a card.)
Turn target creature with a morph ability face down.