So, I use TeXStudio on Mac with MacTex and have a couple of custom commands. I can access them via Tools->User->xxx menu and of course with a keyboard shortcut. But, is there anyway to create a clickable icon in the toolbar for a custom command?
You can do that as per chapter 1.8 in the Texstudio manual.
Menu > Options > Configure TeXstudio > Toolbars > [checked] Show advanced options > pick the Toolbar you want to add the icon to from the left dropdown > pick 'All menus' from the right dropdown > navigate & select your 1st custom command in the right panel > click the left arrow to add that action to the toolbar > right click the newly added action in the left panel > Load other icon > select an icon (perhaps custom made and saved as SVG) > click Ok.
Test and redo with 2nd custom command.