Homebrew Updating games for Citra

[kinghamster]

Hello guys! I would like to ask something regarding on how to update .3ds games without a 3ds device
I watched a video of someone updating his games by extracting the contents of .cxi and .3ds, pasting the contents of the update .cxi to replace the old contents of the .3ds and rebuilding it to finally make the updated game, but i have some questions regarding about this since the comments section is blocked:
1. Can i use .cia files instead? If so, how?
I tried this already but the resulting .3ds is a failure (the total size is invalid)
2. Can i convert a .cia file to .cxi?
I have the update files but they are on .cia, i dont know how to get the .cxi ones, i have some tools especially cxitool but it doesnt work (pasting dlls worked, but i stopped when it said something about entry point blabla...)
Thanks for reading guys!