Yes, you can change the button globally by going to the Settings page or by individual product by going to Products > Settings.
Yes, you can by going to change by going to the Settings page, under Default Settings click on Edit:
Under Button Text you can change the text to the one that you prefer and click on Save:
If you wish to only change the label of the Pre-Order button on certain pre-order product only, please go to Products and click on the "Edit Settings" button:
You can change the text under Button Text: