Flashing andriod roms and kernals If you have rooted an android phone and flashed a different kernel can you just flash over another rom or will it brick your phone. 

Is it necessary to go back to a google factory rom before you flash another rom?
If you have a ROM you are simply updating with a newer version of that ROM, you will need to re-install the custom kernel though. It's usually not recommended to flash one ROM over another different one without wiping. I have not had any experience with my phones being bricked; however, it can cause your ROM &amp; the apps/settings within your new ROM to crash or not act as intended. Dirty flashing is usually only done with updates from the same custom ROM. 

best practice is usually to do a clean install, which would mean wiping data, cache, and system data. This would mean losing all of your personal data, and may also include internal memory depending on device. I would go to your devices' dedicated forum for more details on properly wiping and installing these things, though. 

To answer your other question, you do not need to install a Stock ROM each time before flashing a new custom ROM.