I want to mod the a380 and 747 and 737 so I can get a custom livery for these airlines
a380-
qatar
etihad
british
asiana
b747-
united post merger
b737-
united post merger
garuda indonesia
spicejet
Are the files you are looking to mod props or automata? If they are props, there is no easy way to re-texture them without having the original 3D modelling files used to create them.
However, if they are automata, then you can extract the textures applied to the automata and edit them to show a custom livery, you need to find the FSH textures contained in the DAT/files of the download and use a tool to extract them such as GoFSH. You can also turn automata into props with ease too.