Question: I have an http proxy, which works OK, but there are some address on my lan which provides some web services.

I want to configure my device so that for some range of addresses the proxy is bypassed.

I have tried with 10.0.0.0/8, but it doesn't work!

Answer: 
Yes. This is definitely possible, requiring no modifications or drivers on the PC. As the OP mentions, the USB identification on the phone end is ultimately done in software (in this file <https://github.com/android/kernel_msm/blob/android-msm-2.6.35/drivers/usb/gadget/composite.c>), and it could be modified to identify itself as a standard USB keyboard.

This change would require a couple of things.

1. A modified kernel with a patched USB driver
2. An Android app that could talk to some interface exposed by the modified USB driver.

There is a paper that was published in 2010 titled [*Exploiting smart-phone USB connectivity for fun and profit*](https://dl.acm.org/doi/10.1145/1920261.1920314). It describes using a phone to brute-force desktop login screens. The method they used involved making the phone appear as a USB keyboard.
It's now >six
years later and
somewhere in between someone created the [Keepass2 USB Keyboard
Plugin](https://duckduckgo.com/?q=Keepass2%20USB%20Keyboard) for [Keepass2Android](https://play.google.com/store/apps/details?id=keepass2android.keepass2android).

Wanted to add this
information here for the sake of completeness and because I found
this question *unanswered* and the aforementioned plugin while
searching for exactly something like that.

I haven't tested it myself yet...