Aldo, some of this topic was also discussed in this thread

Unallowing Withdrawal of a Protest

Thanks Ang for referring to the previous post around arbitration.
Since that was a very long discussion and it may be difficult to find there the answer to Aldo's simple question, I am offering my opinion here.

B's post race penalty is an applicable penalty just like a 1 or 2 turns penalty taken on the water. And it may happen that a boat takes a 1 or 2 turns penalty "just in case" even when she's not 100% to be at fault.
So yes, the SCP from post-race penalty remains.

Let me also add that the arbitrator just offers an opinion and - as needed - a post-race scoring penalty. So it is an offer, not an imposition of a penalty, and it is ultimately the party decision whether to accept it or not.
This is just to clear any doubt that the offer from the arbitrator cannot even be grounds for a request for redress by B in case the panel should revert the arbitrator's opinion.

- Claudio

This is how I might look at it ... 

Both Appx T and USS's Appx V offer the ability for a post-race penalty and they are both offered with the following condition ..

After an Arbitration under Appx T .. the 3 of you are standing there like Clint Eastwood, Eli Wallach and Lee Van Cleef in the final scene of 'The Good, the Bad and the Ugly' .. waiting to see who will draw first.

Boat B draws first and accepts the post-race penalty ...  but Boat A does not withdraw her protest and insists on a hearing.  I think in that case, at that moment if Boat B would like to withdraw her acceptance of the post-race penalty BEFORE THE BEGINNING OF THE HEARING .. then fine. 

Boat B would then be opening herself to a DSQ in the hearing and will no longer have the protection of 64.2(a)'s , " .. shall not be further penalized .. ". 

I think that is Boat B's choice and Boat B's gamble to make.

PS:  Which face below best fits the look on the face of the Arbitrator? :-)  (I think Clint's got it)

Ah ah I like this Ang!

But what a gamble for A to not withdraw her protest if B accepted the SCP.
She only has to lose, as B's penalty would not be turned into a DSQ anyway.
A may only gain one miserable point if B was before her in the race and gets a DSQ, what a deal!

When the man with a 45 meets the man with a rifle, you said, "the man with a pistol is a dead man."

C.

If you're going to shoot, shoot don't talk.

If the arbitration is refused and protest is not withdrawn the protest is valid,and game is still on. 
"B" can't be further penalized unless something special will come up.
And if the protest is not withdrawn the hearing will be held, it is up to the panel to decide which boat(if any) is penalized.

instructive and funny. The three shooters example makes me laugh for a good while. Thanks you all

I diasagree with Arto. Once B accepts a penalty, she cannot be further penalized UNLESS 44.1(B) applies because there was serious damage or injury. In that case, I think B's acceptance of an arbitration penalty would be disallowed, and B would be DSQ for the race.