Is there a shortcut for switching between drawing Lines and drawing Arcs in ArcMap?

Go to Customize in your main menu, then Toolbars, then Customize in that list. Now go to commands and wait for the GUI to populate. Go down to Editor and find the whatever tool you are using on the right and hit Keyboard on the bottom. Now find the tool again in the Customize Keyboard GUI (now that you know the name) and assign a shortcut to it.

Assuming you have a construction tool active (e.g. line tool), you can also press TAB to display the feature construction toolbar at the mouse location then select a shape constructor.