This is actually not too difficult but it does require a little knowledge about how the developer SDK works. I would recommend reading the SDK documentation, especially the section about modular simobjects. Modular SimObjects
The strategy we’ll use it to create a new variant of this aircraft to apply the changes. It will inherit all the common configuration data plus whatever you want to change in the engines.cfg.
Create a new Aircraft project in the dev mode. It will have one assetgroup, a ModularSimObject. Give these unique names. In the PackageSources, you’ll set up the directory structure to have one airplane with the same name of the one your modding. Then it will have one preset with a unique name. That preset needs a config folder with an aircraft.cfg, attached_objects.cfg and an engines.cfg. Edit the aircraft.cfg so your variant has a unique title.
You can refer to this project which also creates new variants of some default aircraft. It will show you how all the project files need to be arranged. GitHub - Sal1800/AgNav_and_lightbar_mod_MSFS2024
The key part of the Modular SimObjects is that you only need to change the config lines that you need and these will get merged with the base config. But you do need to start with some files from the original aircraft. To get these, in dev mode, open the Virtual File System window and start mirroring. Now you can browse to the streamed files and copy the attached_objects.cfg from the variant you want to copy and the engines.cfg.
Add those files to your project and make the edits. You need the attached_objects.cfg because this instructs the sim to assemble the parts needed for that variant. Build the project and see if you can select it in the sim.
Some variants need more files if they are specific to that variant. If you want yours to also have those, copy them from the virtual file system. If you get stuck, send me a message and I can help clarify things. Asobo made this type of modding easier than before so just about anyone* can do it. *PC users.