Custom Level Names
This guide will hopefully teach you on how to make custom level names.
Setting up Kuriimu
If you haven't already, download Kuriimu. Use a program like 7-Zip to unzip the .rar file.
Copying the .msbt files to your mod
NSMBU/content and copy your region's folder. For example the "US" folder. Paste it into your mods content folder. Delete all folders except the "English" folder.
It should look like this:
Open Kuriimu and click File > Open.
For this guide we are going to be editing the Course Names. So lets open the course_name.msbt file.
Here it doesn't really matter what you click. If you click "Yes", you can see the original level name. For now, we're going to click "No".
On the left there are all the courses, if you click on them you can edit the names of them. In the middle, you see the name of the course. On the right, you see the original level name if you clicked "Yes".
After you're done editing the level names, save it by doing File > Save.
As you can see, it works!