I was going back to read some old scenes of homestuck and I had some issues because of the retcon stuff so I was wondering if it's still possible to read homestuck with preretcon stuff or is the comic itself altered to only retcon ?

The story in its entirely has changed with little oil and hands spread throughout it. The points that John travels to and messes with stuff have two paths and you can only read the post-retcon path of you have the password from later on in the story.