Originally posted by davey23uk
Think here we are talking about editing the actual file, perfectly possible to corrupt it then

No, not possible to corrupt it using alter system = ... as any invalid parameter wont be written to the file.

although you can make it so your instance doesnt start that way - but the file itself is still valid
Right fair enough, I was a tad hazy on that. Better rtfm if I ever use a SPFILE