2 Questions regarding making a custom carrier [Power, Detection]

Hello there o/

A friend and me recently got ourselves each an Edge and a Captain with the goal of making our own custom carrier (most likely heavily derived from the captain but deviating as time goes on as this is somewhat of a learning experience for both of us). The schematics have been very insightful and helpful so far but Ive got 2 questions:

1) We are contemplating customizing the charging circuit for example which would include trying use the BQ25703A at higher voltages to enable the use of bigger batteries and more range for the DC-Input.
Now with how I understand the schematic I see two problems here: The DC Input voltage range is dependent on the voltage tolerance of VBUS and the battery voltage range is dependent on the voltage tolerance of VSYS. Is this assertion correct and is there a table regarding the absolute maximum/minimum (and recommended) ratings of the Nets in the MXM3 pinout, particularily VBUS and VSYS?

2) On page 8 of the Captain schematic there are some notes regarding the carrier identification. I assume that also controls what devices are looked for and how they get configured. We were planning on modifying the existing Android build, adjusting the Captain configuration to fit our needs. Seeing that theres a configuration option Id like to go down that route to avoid incompatibility or worse damage when putting the Edge back onto the Captain while the wrong build is flashed on there.
Is there some sort of value to configure the resistor to that serves as a general “Proprietary” carrier that isnt linked to any official hardware, that we can use to develop our custom carrier?

(PS: Some general guidance on how and when the carrier detection plays a role within the boot process and how it configures the devices with maybe a few pointers to the responsible files in the source code would be really neat too but I think we would eventually find our way by trial and error regardless if necessary ;D Already customized the fan curve)

Thank you for your time!