You can send a string to your Neo with the following sentence (I didn't check the validity of your bytes):
echo -en '\xB5\x62\x06\x08\x06\x00\xC8\x00\x01\x00\x01\x00\xDE\x6A' > /dev/ttyAMA0
But you need to be under the root user for both side of the ">" character :
if you do only
sudo echo [...] > /dev/ttyAMA0
the echo command is ...
How can Rpi change Neo-6M / 8M GPS measurement/navigation update rates?
The OP uses a python program to change the update rate but has no luck. His python program imports pynmea2 to handle the RMC sentence.
Now I am trying to repeat the python program and see if the program works. I am using Knio's pynmea2 (Ref 37)
In case anyone had the same problem, I had the same situation: using 3.5" LCD and MFRC522 at the same time. LCD driver is this and MFRC522 driver is this.
I added this line at the end of config.txt and it worked!
It seems LCD driver claims GPIO7 & GPIO8 pins.