You don't getting choose whether you do 'not as described' overseas returns.  The buyer has the same rights as UK buyers,  I.e to return an item they think is not as described, at the seller's expense,  for a full refund.

Given how difficult it is for a UK seller to provide an international label,  and the possibility of the buyer simply keeping any funds sent for them to buy a label, a partial refund may be the easiest option. 

Failure to provide a means of return risks a refund forced by ebay, and no item returned.