Easy thing first: If you view your post after you have saved it there is a "Modify" button above it, and that is how you edit things. I'm not sure, but I think there is a limited time window in which you can edit your posts.
Other than that. Yes, you are right, a pwBPD does get so angry in ways that are completely inappropriate.
Your best bet is to just remove yourself from that anger--it won't last forever, and often will dissipate faster with nobody to aim it at. Being consistent with this can pretty much end raging behaviors.
Sadly, the silent treatment may go on way too long and you can't do as much about it. I found reading about it here very helpful to me:
BPD BEHAVIORS: Silent treatment - verbal abuse.