1 - How to Change Serial Number of Dongles
Basically it is done by following command:
rtl_eeprom -s [desired_serial_number]
1.1 - Prepare
sudo apt update
sudo apt install rtl-sdr
sudo systemctl stop piaware dump1090-fa dump978-fa
1.2 - Serialize dump1090-fa dongle
Serialization is done one dongle at a time.
Lets start with serializing dump1090-fa dongle.
Plugin the dump1090-fa dongle, and unplug all other dongles.
Give following command:
rtl_eeprom -s 00001090
The last line of output generated will be:
Write new configuration to device [y/n]?
Press y then press Enter key.
Put a sticker on dongle and write the serial number you have assigned
1.3 - Serialize dump978-fa dongle
Unplug dump1090-fa dongle, and plugin dump978-fa dongle, and give this command
rtl_eeprom -s 00000978
The last line of output generated will be:
Write new configuration to device [y/n]?
Press y then press Enter key.
Put a sticker on dongle and write the serial number you have assigned
1.4 - Un-plug, then re-plug both dongles, and REBOOT
1.5 - After reboot, issue following command to check that serial numbers have actually changed to desired values:
rtl_test -t
And thatâs all 
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2 - BACKGROUND INFO
2.1 - Options to identify a dongle
There are two numbers by which dongle is identified by a decoder software:
2.1.1 - The device number
The device number is assigned by the computer. If there is only one dongle plugged-in, it is assigned device number 0. If two dongles are plugged-in, one is assigned device number 0 and the other device number 1. In case of two dongles, which one gets number 0 and which one get number 1 is randomly decided by the computer.
2.1.2 - The serial number
This is the number saved in memory (eeprom) of the dongle, and is NOT randomly decided by the computer. It is an eight-digit number. Generally factory default for serial numbers is 00000000. This number however can be changed by user and saved in dongleâs eeprom memory.
2.2 - Best way to identify a dongle
When using 2 dongles and 2 decoders (1090 & 978), the best way to identify dongles is to identify these by serial number. This considts of following two steps:
2. 2.1 - Change factory assigned default number
In both dongles, change 00000000, by two different 8-digit serial numers. For example, one dongle is given number 0000011 or 00000101, and the other 00000012 or 00000102.
NOTE:
(a) Please do NOT use serial numbers 00000000, 00000001, or 00000002, 00000003 etc, as it will conflict with device numbers 0, 1, 2, 3.
(b) Do not assign a two or three digit number like 14 or 112. Instead use its 8-digit version 00000014 or 00000112.