Updates not stepping on Custom code

When we first used this plugin, it was suggested to create a new custom php to edit how you wanted individual staff members to be displayed using the file: single-staff-member.php We had placed this in our child theme folder as to not get stepped on by any plugin updates.

A few months ago, this stopped working. Now it seems that we need to modify the file: class-simple-staff-list-admin.php which is located in the plugin’s admin folder. Putting an edited version of the php file in our child theme does not work, the plugin doesn’t recognize it – it must be located in the plugin admin directory in order for the custom code to be visable.

Is there a new suggested method of having custom code so plugin updates will not step on our edits?

Thanks in advance.