Merge files, Add configurations that do not exist, instead of creating files if they do not exist

yes, I think this mod simply won't do anything if the file exist, it should parse the information from the config and check if key values exist in the actual config during the initial launch.

just support a handful of standard configs is definately enough
.json, .properties, special file such as option.txt maybe .toml etc. If none of it exist then fallback to just check if the file exist. But option.txt is definitely the focus here. One problem with this is that some launcher e.g. modrinth they create option files by themselves sometimes controlled via their settings during initial launch, thus causing this mod not to add in preconfigured option.txt when modpack loaded in the first time on modrinth launcher.

Alternatively, we could define a config for yosbr specifying which file should be checked in a this granular way so that modpack dev can specify which config should always be parsed during initial run, this will reduce useless config parsing and be able to target specific file.

Is there no one else who will deal with this problem?

+1 to this, I often create a sparse options.txt file with just my fov and mouseSensitivity changes, and with the current implementation of YOSBR, it will simply do nothing. Instead, it would be really nice if it could go through each flag and set the ones that don't exist. It would honestly be such a nice QOL improvement.