Yes, but why and where you prefer to use CLICK instead of PRESS?
Blender 2.80 has a new way to highlight buttons by using depress
parameter ( Custom
tab):
Vertex button:
L.operator("pme.exec", text=slot, icon=icon, icon_value=icon_value, depress=C.tool_settings.mesh_select_mode[0]).cmd = "C.tool_settings.mesh_select_mode = (True, False, False)"
Edge button:
L.operator("pme.exec", text=slot, icon=icon, icon_value=icon_value, depress=C.tool_settings.mesh_select_mode[1]).cmd = "C.tool_settings.mesh_select_mode = (False, True, False)"
No, afaik.
You mean like this?