Hi Tony

Thanks for posting on the community! Unfortunately it is not possible to change the edges of the button shape on Lucidchart but there is an easy workaround. 

You can create your own buttons by using our shapes library. To do this drag and drop the shape of the button you would like from our shapes panel on the left. You can then edit your shape to your liking in the properties bar. Take a look at this article on modifying and styling shapes.

From there you can make your shape into a button by using Actions and Hotspots. To do this click on More in your properties bar and select Actions. There you can make your shape link to different Lucidchart Documents document pages and layers and other websites. You can learn more about actions and hotspots by looking at the Action and Hotspots article in our Help Center.

If you would like to use the shape of the button you created several times you can just style it how you like and then create a custom shape. To find your saved shape library select Shapes > My Libraries > My Saved Shapes. To create a custom shape drag the shape you wish to add and drop it in your My Saved Shapes library on the left. Now you can use this custom shape everywhere on any Lucidchart document. To learn more about how to create your custom shape library watch this Create Custom Shapes and Libraries video.

Hope this helps!