Can military aircraft send out false ADS-B tracking information? Can most military and VIP aircraft out of Andrews AFB transmit false ADS-B signals?
Here is the ADS-B tracking of Navy P-3 Orion that seems to be violating Iranian air space tonight if the ADS-B is correct. An Iranian fighter was launched heading in it's direction but did not approach it. Two nights ago I was watching on globe.adsbexchange and flightaware the tracking of AF1 was transmitting. It was about 2 miles out from the air field for a landing and the ATC tower noted to ground crew VIP traffic is 10 miles out. It showed it landing when in fact it was still in the air. I know they are allowed to turn off their ADS-B anytime they need to for security reasons.
It is certainly possible, and also happens with some regularity. Here is an article discussing a recent USAF RC-135 flight over the South China Sea in which the RC-135 changed it's Mode S identifier to that of some Malaysian-registered plane.

At some point, the plane’s Mode-S number suddenly changed, from AE01CE to 750548. That’s the ICAO number for an unknown Malaysian aircraft. The RC-135W, call sign RAINY51, then flew a racetrack pattern between Hainan Island and the Paracel Islands, an archipelago in the South China Sea that China claims, but whose ownership is in dispute.

https://ph.news.yahoo.com/u-spy-plane-impersonates-malaysian-130000120.html
Relevant twitter thread linked in the article, with ADSB Exchange screenshots
https://twitter.com/steffanwatkins/status/1303776525083381760