I hope you are well today and thank you for your question.
Yes it’s possibile to modify Call to Action by creating a child theme of Sparkling theme and then overwrite the function sparkling_call_for_action in it and customize it as described in the below thread.
thanks for the answer. What does that code actually do?
What I need is adding pictures to the action bar and try different positions for those images. It should be somekind of a welcome bar, with my photo (like a rounded gravatar) and the invitation to subscribe and get a reward.