What does the GPS firmware do with the acceleration / speed at high altitude build for us to 135k feet?

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The high-altitude change was simply setting the upper limits on a solution from the Kalman filter. It had no effect on how we report altitude or speed or how we handle acceleration.  Therefore, with such a build we still make the same determinations we do in unmodified software: before we report a location the two conditions of the ITAR limits must be verified.

Limit 1: speed cannot be above 1000 kts (514 m/s) when altitude is above 60,000 feet (18288 m) – both conditions must be met at the same time for this to cause position output to stop.

Limit 2: speed cannot exceed 600 m/s regardless of altitude. Since velocities of winds aloft are never expected to reach 1000 kts, the high-altitude build should work just fine for things that are drifting in the atmosphere like weather balloons. However, sounding rockets and the likes do not work as they exceed those limits.