It is very illegal to transmit false location data.
Some older planes don't have GPS enabled transponders so they can only be accurately pinpointed when interrogated by radar. To get a fix tracking networks will calculate the time the signal arrived at multiple receivers and work out the math to ballpark the location.
The deadline for ADS-B conversion was January 2020, so pretty much all of the older aircraft have either been converted, or can no longer be flown without a waiver (which, at this point, will pretty much only be given if you're flying to a shop for the upgrade).
Some older planes don't have GPS enabled transponders so they can only be accurately pinpointed when interrogated by radar. To get a fix tracking networks will calculate the time the signal arrived at multiple receivers and work out the math to ballpark the location.