Using UNIT METER in a REAL attribute in resource files links it the scale tool, scaling automatically when we use it. Adding UNIT METER to a VECTOR works the same way, but it does not respect each individual axis. Scaling only the X, Y or Z axis will scale every component of Vector, not only the axis I'm scaling. How can I apply only the actual scaling axis to the vector?
it's always me, who has to bring bad news to you...
Unfortunately this is not possible, the Scale Tool always scales the entire Vector. As evidence you can for example look at our standard Cube and how it reacts to the Scale tool.
Edit: I have changed the thread into a question.
So it's basically impossible to use each scale axis independently in a custom object?
Is there any other way to get the scaling axis other than using UNIT METER in an argument?
with respect to the Scale tool, yes, it is impossible to have individual parameters of a custom object scaled non-uniformly.
Of course (but I'm sure you are aware, just mentioning for completeness here) such parameters can be scaled non-uniformly via the Attribute manager. Also you could implement handles for such, so the user can access these via the viewport. And the last option could be to implement your own scale tool.
I'm sorry, I know, none of these options is very convenient, but unfortunately I have nothing better to offer.