Geometry collection support uniform scale, while it may be possible to use non-uniform scaling in some case this may lead to problems with how the transforms and collision behave, so we do not recommend non uniform scaling
regarding your attempt to override the dataflow variables, asset dataflow graphs are used to generate asset at editor time, so overriding the variable at runtime will have no effect
For this kind of situation, I’d recommend building multiple walls that can be combined in a larger one ( let say size 8 / 4 / 2 / 1 ) that allow you to combine them to fit mostly any space
This has the advantage also to avoid having texture stretching and keep a more controlled art direction ( if that’s a point that matters in your case )