How to mod bonus tech

[teitokulorentz721]

I am playing as the Japanese and I would like to know how I could mod the bonus tech of an nation.
I am trying to make the game as historical as possible by giving them the tech that they develop first irl

Thank you and Aregato gozaemasu

[aeson]

At the end of the nation definition - found in the appropriate BNat*.dat files for standard powers or in the appropriate *.nat file for a custom nation - add the line "BTL=[tech id]", where [tech id] is the identification number for the technology you want as a bonus tech. The tech ids for all techs can be found in ResearchAreas2.dat; if I recall correctly, the format for each tech definition is:

[Tech name];[nominal year of development];[easier to develop if others developed first Y/N];[probability of being skipped];[cost];[tech id];[description]
So for example if Japan is to be given coordinated multi-carrier air strikes as a bonus tech, we'd find the Coordinated Airstrikes tech in ResearchAreas2.dat:

Coordinated airstrike management;1941;N;70;10;1708;Allows coordinated strikes from several carriers
read the tech ID (1708) from it, and add the line:

BTL=1708
to the end of the nation definition for Japan.

I would advise you to create a backup copy of the original file before doing any modification of base-game files, just in case anything goes wrong.

[teitokulorentz721]

I have found out that adding the line: BTL=1708 wouldnt work but BTL1=1708 would.

Why and why can I only have 4 bouns tech?

Only BTL1;BTL2;BTL3;BTL4 works.

Also is it possible to mod a saved game?