HTL is purely a templating language and you cannot do any logic manipulation in it. You have to either use Java or JS for the same.
If you don't have an associated Java class and this is the only action you want to do with some properties , I will give you a quick tip. In cases like that I always use a Javascript Use-API. For such small things I would prefer JS rather than going a Java route. Refer below link to see how you can write. If you don't get an idea, let me know I will try to provide some sample
https://experienceleague.adobe.com/docs/experience-manager-htl/using/htl/use-api-javascript.html?lang=en
PS:- This is just a personal tip 🙂
Thanks
Veena ✌