To install Kaizo Mario 3D Land into a Citra rom of Super Mario 3D Land
you need to have HackingToolkit9DS - https://github.com/Asia81/HackingToolkit9DS-Deprecated-/releases
You also need a .3DS file of Super Mario 3D Land
Put the .3DS file into the same folder as hackingtoolkit.
Press D to extract the Contents of the .3DS.
When it's done, go into the ExtractedRomFS of your now Extracted .3DS and remove StageData.
Now get the StageData from the Kaizo Mario 3D Land folder and put it in ExtractedRomFS.
Now Press R in HackingToolkit to turn it into Kaizo Mario 3D land and you're done.
You can also Replace LocalizedData, ObjectData and, SoundData but it doesn't matter as it's just some of the music, models and text, only StageData is required.
Instructions 2. 3DS and Citra Intended Way.
Part 1. Citra
Find Citra's folders
go to AppData/Roaming/Citra/User
go to load
you may not have a "mods" folder so many it inside the load folder 
0004000000054000 is super mario 3d land's id so go in there
and put "LocalizedData, SoundData, and StageData" into a folder called romfs.
Part 2. N3DS
For Luma you have to put your 3DS' sd card into your pc
find the "luma" folder
if "titles" doesn't exist inside the luma folder, make one
make a folder inside titles called "0004000000054000"
and then put the "LocalizedData, SoundData, StageData, and ObjectData" into a folder called "romfs"
enable Game Patching with Luma3DS by booting up the 3ds while holding select.