I made a reservation for Portugal in May that I changed to Vegas in Dec in order to hold my reservation fee until I could decide on where to use my points. I ended up booking other vacations and won't want to travel again in Dec. Is there a way to somehow book for 2020 and use the same reservation fee? Does it help if I save 2019 points to use in this new reservation? Probably a lost cause but hoping someone on here may have a work-around.
I am unsure from this post whether you are also worried about losing your points - but it sounds like you may be.
You cannot use a 2019 reservation for anything but 2019. I have tried including talking to HGVC reps but there is not really anyway around it. If you are not going to travel in 2019 (or not going to send somebody else travelling) you should consider the reservation fee as lost. The changeable reservations allow you to do a lot but crossing a year is not one of them.
What is far more important than losing a reservation fee is losing a reasonable number of points. If you are using 2019 points in the reservation you could lose those. If this is the case, i would cancel the reservation and pay the fee to "rescue" those points and any other remaining 2019 points. Of course this all assumes that we are talking about enough points to justify the rescue fee.
Good luck !