Many locals have started transitioning to UCF, but it does not alter angles the way you seem to think it does. The first main change is it gives you an extra frame to dash back. Pretty much all controllers have at least 50% consistency with smash turns, and if your controller is older/worn in, it's possible it has even better consistency than that. Even if you practice without UCF, you are likely going to be performing the dash the same way regardless, so that won't have a huge impact on you.
The second main change is it prevents spotdodging when using the lower 45 degree notches for shield dropping. If you practice without UCF, you will probably have to be much more delicate with the precision of your stick by stopping it before it reaches the notch in order to shield drop properly. This type of input is slower than relying on the notches as is customary in UCF, but whatever motion you practice for shield dropping on vanilla will still work on UCF. You just won't be taking advantage of the notch method as much as people who have practiced on UCF.
I don't think you can use it on 20xx, but I would not be surprised if the release an updated version of 20xx relatively soon with UCF codes built in. Alternatively, I think you can use a vanilla iso on your Wii and load UCF with that. And of course, you can always go buy a copy of the disc and start your Wii normally. All in all, practicing on UCF is not going to change that much for you, it's pretty much just shield dropping. It's important at medium-high levels, but if you're a relatively new player it will hardly affect you at all. You can still practice any other techniques that involve angles and they will work the same on UCF as they do on vanilla.