Spot on there, Nor. However, that is in theory. If the application supports more than one instance of it then it is doable if you can modify the port on-the-fly. However, if each instance shares the same configuration file and update on-the-fly then you're going to inevitably run into problems with that set-up.
For this to work without any problems, the application should really claim to be able to run multiple instances, and any attempt at circumventing the aforementioned and making it work, would be pure luck - plain and simple. For it to work when it's not supposed to, the configuration files will have to be edited before each execution of the instance - and with a little luck in that the first instance doesn't recognise the modification to the configuration file.
After saying all that, I'm sure something as big as XAMPP would allow multiple instances and also allow you to bind those instances to different ports. First stop - the XAMPP website!
The man who comes back through the Door in the Wall will never be quite the same as the man who went out.
well just open multiple instances of apache each listening on a different port, it will work if you create its own seperate dir with its own config etc not sure if there is any other way (in other words have multiple apache webservers running), i still think that using one apache and using a virtual host is better i.e.: