I have not tried but have had thoughts about it the same way you have.

The theme files work mostly in the same manor the icons do.. ie. your current theme are the ones used if existing else it use the "base" stock ones. Similar to hicolor for icons. So a safer way would be to copy those files to the blanco theme rather than change the base theme. It would also make it easier to revert as a simple "rm" command would work.

I have however notices some bugs on this where it doesn't work and the base theme need to be changed. I do not know how the transitions apply to this though.