Make one thing act like another

[Zman350x]

I have a long list of 750 single digit numbers.

WorldList = [0,0,3,7,3,2...]

I use the variable valIndex plus a number to call certain points in the list.

WorldList[valIndex + 30] = 0

I know that I could use an if statement every time I call a point, but could I make something at the top of my code that says "anywhere in the code where valIndex is a multiple of 30, set WorldList[valIndex+30] to 0"

so if I set valIndex to 60, then WorldList at 90 acts like 0. But as soon as valIndex changes, WorldList[90] goes back to what it was originally.

I know this is confusing and probably doesn't make sense.