This changed over 20 years ago, GPS no longer has artificial limitations for accuracy.
You can't get commercial GPS receivers licenced unless you restrict the altitude and speed they operate at, but a dedicated self-built receiver technically doesn't need to have these restrictions. There are SDR+software projects that do this, which could technically be used for ICBM guidance with no restrictions.
The restrictions are for high speed and high altitude, not accuracy. You can use the GPS module at full accuracy if you aren't really high or going really fast. Model (high-powered) rocketry trackers occasionally run into this, but usually not an issue since you need the location data to find where it lands, and it's going pretty slow under chute.
(Maybe you should read why GPS is not more accurate: it's not a technical limitation, it's done on purpose.
Also try to read up on Chesterton's Fence.)