We design the snake to look like this, and the bird to look like that, and the human figure to look like this other. Does it have to be exactly like that, or can we have some freedom when designing a font for Egyptian Hieroglyphic orthography? Could the snake be in a different pose? The bird facing a different direction or with different features? The eye a full eyeball, stuff like that? Basically as long as it gets the image essence across, is that acceptable? I'm wondering how varied the orthography is across different specimens, or if it is as consistent as our computer-printed latin orthography so to speak.
Like with all writing systems, a certain amount of variation is natural and expected. What's important is that the sign not be confused with any other.
Here's the beginning of Gardiner's sign list again:
As you can see, A1 ("masculine determinative") can get pretty stylized while still being recognizably A1! What's important is that the hand not end up pointing to the mouth, which would turn it into A2 ("eat/drink/speak"), and that the heel of the back foot not be raised, which would turn it into A3 ("sit"). And people making monuments often did vary the shapes of individual signs for aesthetic reasons.
For an extreme example, look into hieratic writing, which originated as a cursive form of hieroglyphics to be written on papyrus. There's still mostly a 1:1 mapping between hieroglyphs and hieratic characters, but the forms are tremendously simplified to be written with a reed brush rather than carved on a monument.