It does seem like it would work. Put a more modern LNB (the front end of the satellite) on an older dish and voila, you’re all set and you don’t have to aim anything or drill new holes. Except, it doesn’t (except in two circumstances I’ll tell you about below.)
If you have an old round dish or an older satellite dome, you might be tempted to buy a more modern LNB rather than installing a whole new dish. If this is an RV or marine installation, you may think this will save you thousands of dollars. The problem is that it doesn’t work. Newer dishes are shaped specifically so that the new LNB will get full signal. There’s no way that a frankensteined dish is going to get all the signals you need, especially if you’re trying to fit a more modern LNB on a round dish. There’s a reason neither DISH nor DIRECTV use round dishes anymore… they need the extra real estate in order to get signals from multiple satellites.
If you really had it in mind to do this, you’d want to make sure you had a good satellite meter, some metalworking tools (because you’ll need to make the arm longer or shorter) and plenty of patience. Unless you already have that stuff, it could potentially be cheaper to replace the dish.
If you do already have a DISH or DIRECTV oval dish, generally you can just change the LNB. This is great for people who are considering a move to 4K or who simply think their LNB has broken. (Hey, it’s a sensitive electronic instrument that sits outside all day. Of course it’s going to break eventually.)
I’m talking about these dishes:
Basically if you’re getting HD service now you can probably swap out the LNB.
If you’re not sure whether an LNB swap is the right choice for you, the best thing to do is call the friendly folks at Solid Signal. They can give you all the details and recommend the best upgrade for you. They’re only a phone call away at 888-233-7563!