Xencelabs Technologies Ltd.

Yes, you can change your Brush size and Brush Hardness (Feathering) simultaneously. 

This will require a combination of keystrokes and a mouse click. 

Windows command: Control + Alt + Right click

Mac command: Control + Option+ Left click

You may be wondering how to combine all of those keyboard presses and mouse clicks into a single button press. The instructions below will walk you through creating this helpful feature.

I'll first show how to do this on the Windows platform.

** Instructions for adding an application to the Application row: https://solutions.xencelabs.com/en/support/solutions/articles/67000544218-how-can-i-make-custom-settings-to-a-specific-application-

What Xencelabs devices will this work with: Pen Tablets, Quick Keys, and Pen Displays.

You will first need to open the Settings panel. [1] I have added Adobe Ps to my Application row and clicked on the Ps icon. You will notice that the Yellow bar is now under the Ps icon. This tells us that any customization we make now can only be used when Ps is the active application. [2] I have selected the pen that I use. [3] I have assigned this feature to the lower button on my 3-Button pen.
Now, we are going to walk through the process of setting the lower button on your 3-Button pen to allow you to easily change the size and hardness of your Ps pen. You can use any button on the 3-Button or Thin pens or a button on the Quick Keys as well. It is up to you where you would like to assign this function. [4] Select your application; I have selected Ps. [5] Then you will need to select the device you want to assign this feature to. I have selected the 3-Button pen in this example. [6] Click on the button to which you want to assign this function. I have selected the lower button on my 3-Button pen. From the drop-down menu, select modifier.
Once you have the Modifier utility box open. [7] You will need to check Alt, Ctrl, and Right Click. [8] Once you have made your selection, click OK.
[9] The new feature has been assigned to the lower pen button, and you are ready to use it.
What it looks like on the Mac Platform:
The process is exactly the same on the Mac. Open the Settings panel. [1] Select the application you want to assign this feature to. [2] Then, select the device and button you want to use. [3] In the Define Modifiers box, check Option + Control + Left Click. Then click OK, and you are set.