Solutions:

Simon at PG jumped in for some more help.

The reason I could not see _BLANK as a style option is that I had my Style picker set to display RTs only. Once I cleared this restriction so that all RT, RM and M styles were shown, the _BLANK options showed up.

He also noted in the Style Picker that I could build something like this from scratch and save it a a custom style for quick reloading.

He also suggested actually making a SONG like this and saving it as a song for my purposes so that I would not have to mess with styles in the future.

He also reassured me that ERASING anything in the mixer just made changes for that song and did not change anything in BIAB (well that sure makes sense!)

Thanks everyone!