Hi,

From what I gather, it is unfortunately not possible to add new icons to the toolbar buttons. According to the K2 smartforms documentation (K2 smartforms > K2 Designer > Views > Creating Views > Layout > Toolbox > Controls > SmartForms- ViewControls - Toolbar Button), under the "Considerations" point 3 states:
There are 12 customisable icons that can be used (these icons can be extended on the back-end)

My guess is if you build a custom theme, you can specify custom icons should be used for Add, Delete, Edit, Save, etc.

Thanks,

Khanh