you are right. since your test variable is equally spaced, i.e., { 2 4 6}, so all contrasts written like the following forms
Linear -1 0 1 & Quad 1 -2 1
were correct to test linear & quad trend.
we know that the constrast does not matter about a factor added, for example {-1 0 1} == {-1.234 0 1.234}, and so on.
Jingju