Hello Helen
Yes, this is something that can be achieved, as was done in the lesson. There is no restriction to keep the translated address in the same subnet. In the case of the lesson, this had to be done because the device whose address is being translated is directly connected to the outside interface of R1. On the Internet, for example, you could translate to any other public IP address.
Another useful application would be to translate the IP address of say, an external web server, to an internal local address. This is what I mean:
Imagine you are H1 and you want to access the web server. But for some reason, H1 is not allowed to access any external hosts, say for security pruposes. You can create the following:
ip nat outside source static 204.123.123.55 192.168.1.55
This allows H1 to communicate with 192.168.1.55 on its own subnet. R1 will receive such packets, and translate and send them over the Internet to the web server. When they come back, they will be translated again, making H1 think that it is communicating with a device on its own subnet.
Just another use of the specific feature.
I hope this has been helpful!
Laz