It's not possible to overwrite the existing EIC code in a NIU but it's possible to erase the programmed EIC code in the NIU and set a new one afterwards.
To erase the programmed EIC code in the NIU board you have to downgrade the firmware to revision R6A.
In the next steps and example I'll show you how to erase the programmed code in the NIU.
As said before it only works in the firmware R6A. This is because we need to use the "invalideic" command that's not there in newer firmware. It could be there by mistake but as it is usefull to clean the EIC code and reset it to ff-ffff.
Because its only there in the firmware R6A you first have to downgrade the NIU board. After the cleaning you are able tu upgrade the fimware to the latest revision again.
The example below show how it works in firmware R6A:
A NIU with EIC code 13-0671 is cleaned (to ff-ffff) and after that programmed with 13-0000.
username ? > MDUSER
password ? >
niux > readeic i
eic account
eic ipa (hex)= 0671
eic as (hex) = 13
niux > help
exceptioninfo: Get Exception information
invalideic: invalid eic information
writeeic: write eic information
readeic: read eic information
eicpinfo: address for eic program
nifrev: display NIF revision
readrof: read the board hardware information
continue? <y>
niux > invalideic 1
niux > readeic i
eic account
eic ipa (hex)= ffff
eic as (hex) = ff
niux > writeeic 0000 13
eic ipa (hex)= 0000
eic as (hex) = 13
Confirm changes?

es or

o <no> y
niux > readeic i
eic account
eic ipa (hex)= 0000
eic as (hex) = 13
niux >