On my 99 impreza L, the two black plastic/hard rubber inserts on roof that run front to back & rain gutter? do these channels that hold plastic, run all the way down beside glass on the pillars? Or do they terminate at top of windshield? Does the plastic strips have a purpose or just cosmetics? Do they pop out, when pried on?

should be some sort of allen or star screw maybe hidden under some sort of cover....

Those rail trim pieces are just that. trim pieces. The problem with removing them is that they go from the base of the windshield to the top of the hatchback lid. At least they did on my 98 impreza hatchback. 

Mine were held on only with plastic clips that slide either fore or aft to un-clip if I remember correctly. Underneath the plastic trim bits you should find the factory mounting points for a roof rack... the primary reason I took mine off in the first place.

 

hope that helps.

So the goove in metal, goes all the way to the bottom base of winshield & conveys water travel?