SamyGO

Yes. Welcome to the brick-land graveyard.
Unfortunately, there is no much options...

A) Remote controller detection blinks does means NOTHING.
B) Your only hope is ExLink cable. Will explain later...
C) I think it's not possible. Because there is nothing wrong with FW but it's settings.
D) Easy way.

With exlink cable, you needed to get in to bootloader.
After you needed to change that settings partition with original partition image that placed at USB disk.
Than tv will powered up. This method could also repair wrongly flashed FW...

Problem is I don't know that where is that panel information stored at TV. Needed to reverse engineering here. Or any one know that?
Might be it placed at /mtd_rwarea ?

I insist that you can recover your TV but I don't know the way exactly.
So I chose D

Rest In Peace brother.
I will cure this torture by killing your hopes.

a) Red dot blinks. Because TV tries to start, load required things until loading exeDSP. When exeDSP loaded, TV crashed.
b) AFAIK Bootloader is available if you chose debug at Service Menu. But I am not sure about that, it might be work if you don't set to debug too...
c) Factory Reset doesn't solve your problem. Because even factory reseted TV needed to know it's correct ID, which you changed. Debug menu will not work you because I am suspecting that your exeDSP crashed. Which debug menu is in it.
d) 9 byte string? What is that? Whatever it is, it will not help.

Your only hope is top TV at bootloader and you cannot get in.

..and since i'm unable to reach service-menu (the LCD is black and -i suppose- not even powered on), i've no hope.
But I still not understand a thing... with a virgin TV ,you see some bootstrap log via ex-link or you see nothing at all (...and to see something is strickly needed to modify options in "service menu")??
here we speaking about LExx550B ,but the question is valid also for 650B..

You can see strings if you enable "debug" on RS232 port. I think you can enter bootloader menu even if you don't enable debug on TV options. This require ExLink cable...
If you say that your TV failed because of changing model type, might be service revive your TV and you could pay less price for repair...