Specifically it decrements the TTL of routed packets, so hotspot traffic will tend to have a TTL of 63 instead of 64. You could theoretically disable this at the risk of creating infinite routing loops, although android probably makes it inaccessible if the kernel has a setting for it at all, so you might have to rewrite packets in user space.

It has been a long time since I've done this, but:

If your Android is rooted, it's pretty easy to get tethering working. There's magisk modules that can fix the TTL problem and/or disable the hidden carrier-installed software that Android will ask for permission before enabling tethering.

Different applications on a single device can't apply different TTL's? I thought TTL was a pretty basic knob exposed to applications. e.g. A sensor that transmits fresh data every 20 seconds doesn't need stale packets bounding around clogging up the pipes, while a file transfer over an intermittently delayed link might benefit from a higher TTL.

> voluntarily tags

Aah, you mean ‘snitches’. :P

Voluntarily tags specific TTL values much like your home router does. Some providers assign a different IP to hotspot users.

Super easy to spoof too.