I would still prefer a one shot remedy instead of pulling a temporary stopgap measure. The more times you try, the more resistance you get I think. Better to do it right when everyone is willing to be on your side, which leads us to how to design the referendum questions right the first time.
The referendum needs to let the people know what choices they have, and at the same time find out if they want a flag change regardless of the choices offered to them. I have two proposals.
Phase 1 Referendum: Do you want the current flag changed?
Phase 2 Referendum: Preferential Voting of the short list candidates and a separate "none of the above" option. A voter's short list candidate preferences is nullified if the separate none of the above option is chosen.
If the majority of the voters passed the phase 1 referendum but chose none of the above option in phase 2, then phase 2 will be repeated at every major election until people finds a flag they like.
Phase 1 Referendum: Preferential Voting of the short list candidates
Phase 1 Referendum: Two referendum questions, 1st, choose between the current flag and the winner of phase 1. 2nd, do you want current flag changed?
If the flag from phase 1 has the majority, it becomes the new national flag. If the old flag has the majority, but the majority also wants to replace the old flag with something else, then the entire referendum will be repeated at every major election until people finds a flag they like.
The difference between the 2 is that in Proposal B, people would know which flag would replace the current flag when they decide if they want the old flag replaced. However, when a new flag isn't chosen the first time, proposal A only needs to repeat the phase 2 referendum.