Are those lines 0-width lines? Try making them a bit wider, thin lines can disappear when output to an image, which again would prevent them from having any effect.

Originally, the dialog had you input numbers from 0 to 8, but people found that confusing so the scale in the dialog was changed to a more familiar 0-100 scale, but the effect still uses the original scale internally.

Looks nice, but that road in the top right part looks a tad to compass rose straight. Would look a bit more natural if both that and the bridge was on a bit of an angle.

I don't think there is a way changing symbol references using macros. But as a workaround, you can just explode the symbols in the drawing. In most cases, this won't make a visual difference, but the symbols are now just a collection of primitive entities which should react nicely to color changing commands. Obviously, they no longer will be regarded as symbols for commands operating on those, but that is usually not that big a problem.

Trim does this when operating on splines. The reason is that the shape of the spline is dependent on the positions of the nodes, including the following nodes, so if you simply cut it and placed a node at the end, the shape would change.

Since CC3+ is a CAD program, having the rest of the shape change shape isn't really acceptable, so instead when you trim a spline, it just hides the rest of the shape instead of removing the nodes from the entity.