Hi @Heinrich,
There are three ways I usually go about this, each of which is worth knowing.
Method 1: Customize First, Then Add More Variables
When you add additional Y variables to your Y-axis they will inherit the properties of the graphs before them. So, with just a single Y variable on your Y axis, make the customizations you want, and then bring in your additional Y variables and they will also use those settings. This will work for all element styles, as well as customizations you made in Right Click > Customize.
Method 2: Broadcast Changes to Elements
If you're just changing element properties/styles, you can broadcast a change by holding down the control key (or the command key, on a mac), and then Right Click one of the plots, then make your change. This will "broadcast" that change to other plots in Graph Builder. Note that you need to do this by right-clicking the plot, not in the elements control panel on the left. Also, this method will not work for customizations you wish to make in Right Click > Customize.
Method 3: Copy Customizations, then Broadcast Customizations
To standardize customizations you make in a plot (using right-click > customize) you can use the same broadcast method, but after copying the customizations. Right-click the plot you have customized > Edit > Copy Customizations. Next, hold the control key (or command on the mac), then right-click any plot > Edit > Paste Customizations.
I hope one of these methods helps!
@julian