Yes, the donation button that you see at the top of your campaign is customizable or you can hide it all together. In your dashboard, click the drop down arrow and select Edit Profile.

Then, click Donation Button on the left-side menu.

Finally, you can 1. Choose to show the donation button. 2. Replace the button text with your own and 3. Choose the campaign you'd like the button to link to. Click Save and you're done!