Some concepts from this guide might carry over to PC Port, but you are better off looking at guides that specifically apply to it.
For simple "Green Stars"-esque hacks, Quad64 might be sufficient as it can edit object placements.
The way the levels in Mario 64 are laid out makes it prohibitively difficult to edit the geometry.
It is faster to just rip the corresponding level from SM64DS Editor or Quad64 Level Ripper, and manually fix it up in Blender.
Turn on Backface Culling in Blender, or the equivalent setting in your 3D modeler, then flip the incorrect faces.
Your game has a bad checksum, navigate to Tools -> Recalculate Checksum in ROM Manager.