[woodslanding]

Right now it is very cool that if I set the pen to perfect white, and give it a large width, I can use it like an eraser that will affect the original PDF, not just the annotations.  And I like how it changes to match the background tone.

But it is clumsy and time consuming to change both the color and the size of the pen to do this.  And then change it back afterwards.

It would be really nice to have an option to make the regular eraser work this way.  Obviously you'd need to be able to turn it on or off, but I do 90% of my annotation erasing via the undo key, so I don't use the regular eraser very often.  Whereas the need to erase something in the original chart happens all the time....

[McAroni]

You could save every preset for your pen or other Tool in the favourites. After setting up your pen Go to the Star ar the top panel and press the plus Icon. You will have access to your saved favourites there, or through the command Bar. 
If you have an spen you could sign the Button to switch to the eraser, and if you release the Button it switches back. This is in my opinion the fastest way to access and leave the eraser