Is it possible to append without changing the index?

[joseph]

I want to add some files to wim without extracting all of them.
wimlib-imagex append always creates index 2. Is there any way to add files to index 1? --rebuild option didn't work either.
It is okay that modify an existing wim, or also create a new wim by adding a few files to the source wim.

[Tokener]

A solution might be:

wimupdate, or equivalently wimlib-imagex update, modifies the specified IMAGE in the Windows Imag-
ing (WIM) archive WIMFILE by adding, deleting, or renaming files or directories in it.