What's happening here is that UA provides several different ways to calculate the fare for the rebooked ticket, depending upon several conditions. The line that you're reading is part of a "keep the fare" group that would allow you to make certain changes without having to reprice the entire ticket.
If you're just looking to cancel the whole thing and replace it with a new booking, the very first rule applies:
Code:
QUALIFYING CURRENT DAY FARE
CANCEL OF TICKETED RESERVATIONS OF A
WHOLLY UNUSED TICKET / CHANGE TO 1ST
TICKETED FLIGHT COUPON
--
REPRICE USING --CURRENT FARES-- IN EFFECT TODAY
--
PROVIDED ALL OF THE FOLLOWING CONDITIONS ARE MET-
1. UA FARES ARE USED EXCEPT EOU/ERU
2. FARE BREAK POINT CHANGES ARE PERMITTED
3. VALIDATE ADVANCE RESERVATION REQUIREMENTS
4. ADVANCE RESERVATION/TKG IS MEASURED FROM
REISSUE DATE TO DEPARTURE OF PRICING UNIT
EOU/ERU are Basic Economy (Economy One-Way Unbundled and Economy Round-Trip Unbundled). So, that's saying, if you haven't used the ticket for anything, you can make a change to any valid fare other than Basic Economy, using current fares (as of the date of change).
I have not, personally, changed a domestic flight to an international one (I've done the reverse). However, given this text in the rule, I'd be confident that it wouldn't be a problem, within certain boundaries: I don't know if you'd be successful in changing it to a fare with a non-US
origin, since the currency would be different. But I don't anticipate any problems changing to a US-origin, international-destination fare.