In KOTOR 2 it's actually possible to remove most of GUI elements (including names above NPCs and placeables) by deleting structures named "BORDERS", "CONTROLS", "EXTENT" from the file mipc28x6_p.gui. KOTOR I probably uses this or similarly named file for its GUI. But like La Ingobernable said, switching between combat styles, using grenades and Force powers without UI is impossible. Maybe you can use hotkeys for some actions, but I doubt.
Here is reworked file from KOTOR 2 for reference.
mipc28x6_p.gui