After you clone "Unix Assembly", did you manually set the mode of the already open .s files? (Document>Select Mode). After adding/moving the .s extension, the Options dialog isn't smart enough to set the mode.
Also, after the clone, does the "Defs" tool window display any symbols?
I'm seeing _point(), _reset(), _reset, __reset_micromips_isa, and __reset_switch_isa in the Defs tool window using the clone of the language (I called "Unix Assembly MIPS").