Any Trigger effects are ignored
Effects that modify a creature's power and/or toughness, such as the effect of Appeal to Eirdu, will apply to the creature no matter when they started to take effect
Hyena Umbra, meanwhile, is a piece of armor thats cheap to play and easy to recur, with a relevant keyword to boot
While its attack, Full Moon Rondo, is situational, its ability, Fairy Zone, may be useful in certain situations
Probably not directly related to its name anymore with that art
This is very different from, lets say, custom alter cards, as the art on those is the property of the people who make them, and also, you know you arent buying a real card. Play it safe if you print the back of an MTG card and put a custom-altered version on the front, and restrict its use to kitchen table rules