Adjusting intensity of baked light.

Is this even possible to tweak intensity or color of a light/emisive mat when it was baked on static or stationary mode?
As a refrence i can show old HL1 (on the right) screen flickering:

Not for emissive materials, but there are several things you can do. If you have a stationary light, changing the intensity during the game will also affect the indirect lighting. You can change the GI intensity/color in post process, but this works for the entire screen. In your example, that might actually not be a bad idea since you’re in a small room and you probably won’t mind the pitch-black look.

Indirect lighting for stationary lights is not something that can be changed during gameplay, you can adjust the intensity/color of the light but it only affects direct lighting.

^ Can confirm this is true. Anything lit directly in the path of this light will change its color properly, even after a bake, but indirect lighting will remain unaffected.