You shouldn't have to use JASS. Just hold shift and double click the unit speed. That makes WE ignore the rules for that field and you can enter almost any value. Whether or not the game will allow speeds faster than 522 is a different question (you may be able to enter 1,000 as the unit speed but the game may still clamp it back to 522).
You could always give the unit unholy or endurance aura and hide the buff. Then set the movement speed increase to whatever and there you go. Don't forget to modify the aura so it only affects "self".