No idea about if you can change your original payout method but because of the huge numbers of claims I doubt they will want to have to ask & readjust it all again.
There is no original payout method, it was just a survey.
All payouts are going to be in Yen unless they decide they will allow payouts in Bitcoin, they stated that if they do allow payouts in Bitcoin people will be asked again for their preference.
Here's a screenshot from the original claim form showing exactly what it said :
oops, my bad above then.