Okay, this is going to be really dirty because I am trying to recall events that took place back in like July when I pulled an all nighter. Basically, this is what i did to edit textures inside of lz files that are used by the UI. This is very limited because Nintendo is dirty as well.
(THIS IS NOT SOME TUTORIAL, JUST NOTES ON WHAT I FOUND IS POSSIBLE TO DO WITH LZ.BINS)
You will need the following (google these, I'm too lazy to get these for you; this is just a list of things that I mentioned in old logs, most of these should apply if you plan on doing some large overhaul):
png2bclim
some darc (de)compressor (idr if pk3ds works or not, I think it might have been one way or something)
msbt editor reloaded (one that has all the (de)compressors working, latest should be fine)
every file explorer (there is a thread somewhere on here with this)
image editor
hex editor
ohana3ds and ohana3ds rebirth
Basically, what you want to do is take some lz of whatever you want to edit that is part of the home menu (I will be using sleep_lz.bin as that was the one I spent a stupid amount of time editing)
Use msbt editor to extract the file as lz11. You will end up with a file called sleep_lz.bin.bin, throw this into new ohana to extract files from it. bclim are texture files, bclan is for animations (you cannot do much with this afaik, maybe you can with the sdk, but I don't have access to that), and bclyt are for the UI (you can open this in EFE to see changes without installing the cia each time. Note that these previews may not be accurate). Sleep_lz textures are not tiled, but instead stretched I guess is the word. (the pixels look normal vertically, but horizontally, they are stretched out)