@brower Thanks very much for your question. If I understand your question correctly, you’re referring to calling code to execute after the user presses the chevron (i.e. the arrow) on the UITableViewCell correct? If this is the case, my guess would be to include the code inside the prepareForSegue method. I would like to point out here that it would not be recommended to make a distinction between a user pressing the accessoryView vs pressing the cell itself (i.e. the contentView). The space is very narrow, and have multiple triggers inside a UITableViewCell would be confusing to the user. In fairness, the accessoryView is just that, an “accessory”. Meaning, it assists the user to know that there is more content available if the user selects the row.
Try to ensure that your UI/UX is simple, and easy to follow so as to not confuse the user. If what you’re trying to do is coming across as being too complex, my guess would be that you should take a step back, and try to simply your workflow. 
I hope this helps!
All the best!