You should always try to adjust the weight on your car so it is equal front/rear and equal
left/right. This will help to ensure proper, consistent handling. You can use balancing tools
to check the weight distribution of your car, and to ensure that your ready-to-race car
does not list to one side or one end.
Examples of balancing chassis weights (front, rear, center)
A simple balancing tool can be a set of stands with points on them. You would then
place the chassis on the points of the stands so that the stand are along the car’s
centerline at the front and rear. If the car lists to one side (for example, to the left), add
weight to the other side (say, to the right) until the car stays level when left untouched.
You can do this also to check front/rear balance by putting the chassis on the balancing
stands on the left and right sides half way along the length of the chassis." - taken from the set up guide that of hudy.
From this I assume adding weight and tweak are two different things.