I think many of us for various reasons have moved a holiday, forwards or backwards.
There is no problem in doing so, although you will probably have to pay a booking amendment fee.
There is no real definitive answer really, if there is a reason why you want to move the dates, then go for it.
Yes I changed my complete holiday this year, got charged £30 each for admin fees but saved myself over £600 so not such a bad thing, and it was very easy to do