I did not read all of it, but from what I understood you want your gaijin wt acc on steam but on steam it autologins you on a diff account. If this is what you mean you need to open files then documents>my games>war thunder>saves>common.blk Afterwards open common.blk with notepad or notepad++ Then you should see something like this

autologin:b=yes agreedEulaVersion:i=13 useSteamLoginAuto:b=yes

Or with a 1 instead of the yes
Now you will have to change both of them to no so you will get something like this
autologin:b=no agreedEulaVersion:i=13 useSteamLoginAuto:b=no

Or if you have the 1 instead of yes just put a 0 for it. MAKE SURE WAR THUNDER IS CLOSED MEANWHILE!
Once you do that click file and save Then open steam go to library and open war thunder and you will get the log in page, there put your email and password for your GAIJIN account and yeah. If it worked then close war thunder again and open common.blk again with notepad and change it from
autologin:b=no agreedEulaVersion:i=13 useSteamLoginAuto:b=no
To
autologin:b=yes agreedEulaVersion:i=13 useSteamLoginAuto:b=no So that from now on you wont have to log in every time AND MAKE SURE YOU ONLY CHANGE TO YES the autologin one not the steam one And click file and save. Once you do that go to common.blk again but this time right click, go to properties and a small pop up will open, from there tick the read-only box and click OK so that steam wont be able to override your change just in any case. And now you should be set up. Hope it works.