Our friends have AONE3 issued and started in Korea and we are now in half way (Asia-> Europe->USA).
Since I have AONE4 including South America, my friends want to change their tickets, and go to South America with me, so their tickets have to be reissued as AONE4, from AONE3.

Now, we realized the price from Korea went up.
Do they still pay only reissue fee, the original price difference of AONE3 and AONE4, and taxes?

or do they have to pay the difference of original AONE3 and new AONE4 price which is significantly higher than original AONE4.

Thanks in advance.