I'm sorry for asking that for the 100th times but i don't wanna get bricked.
If I installed via the blue card the 2.0b2, never opened gateway (it crushed twice and I removed the SD), and I replace the launcher to 1.2 launcher, without reinstalling, will it be okay?
You don't install 2.0B2 from the blue card, you only install the exploit itself (The change that allows your 3DS to launch the "Launcher.dat" on your SD card). Replacing your "Launcher.dat" on your SD card with the 1.2 version will stop the risk of your 3DS bricking.