The sequence you are looking for is 1520 3 x x -value, not literally the example sequence I gave. You can try find all "1520..." sequences and identify the right one ENDING with a negative number. If the code is more complicated and there's no negative value anywhere at the end of the sequence, then they use variables and it's too complex for you to do anything.
That -2 you changed to 0 is part of another instruction, you simply don't know what you are doing. It's probably part of a calculation to determine by how much to increase or decrease attributes, using a variable to store the value.
This is what happens in pseudo code:
change = change * (-2) // 2107 2 1224979098644774913 -2
change_some_attribute by (change) // 1520 3 ? ? 1224979098644774913 (it's a guess, since you cut off the instruction)
Anyway, if the same code both raises and lowers attributes (as above), and you want to keep one but get rid of the other, it's much more complicated to accomplish this. If you multiply the change by 0, you'll always get no change, as you found out. Just live with it.
Edit.
You are right and this is futile anyway.