When you change a flight a the new flight costs less than the currently booked flight the price is shown as a negative. Completing that change will generate a new travel fund for you and that can be applied just like any other travel fund to the purchase of a flight. That can be one of 3 payment methods used to complete the purchase.
It is possible to combine travel funds if you have 3 that combined together would cover the purchase of a flight. For example, if you have three travel funds: $20, $25, and $5 for a total of $50. Find a flight that costs $50 or less and book it with the 3 travel funds, then cancel it and you will have a single travel fund for the amount of the flight you just booked and cancelled. Doing this will create a new fund with the expiration date of the earliest expiration date of the 3 travel funds you used to complete the transaction so just watch out if you have any funds expiring much sooner than others. You can repeat this process as needed to combine as many funds as you want. I have used this method to take 10 or so smaller travel funds and make one large one.
--TheMiddleSeat
