Hello,
Thanks for the detailed description. Much better, then "I need to customize web-site" and that's all :)
Ok. I can create a custom wordpress plugin especially for your web-site which will provide you with this feature. So, I won't edit template or core wordpress/woocommerce files. You'll be able to activate/deactivate this plugin.
To investigate how it is currently setup, then create plugin which will check (via ajax and via formsubmit) which product is chosen and add necessary html(notification/comment) --> all together will take 2-3 days and my cost is 222usd.
I can start tomorrow. Today I'm finishing another project.
If you have questions, please be free to contact me.
BTW, I'm Serhii Kniaziuk, a php/js/wordpress developer with 10y+ experience. More about me you can find here: freelancer.com/u/serhiikniaziuk.html (including feedback from last employers)
BR,