to update with my experience. I called in (and HUCA) and was told no way to change award origin, or to hold a new ticket whilst the miles came back. Only option is to cancel and wait for miles. 20 euro fee each ticket (no mention of a call center fee)
The miles actually came back within 24hrs but unfortunately the flight I really wanted had already gone by then, but got one earlier in the day from my preferred origin so not a big deal. At least now if it opens up and I want to change this will be possible - as date or time changes are OK.
My trip is very far out and plenty of other options were workable for me worst case, I would be very nervous with this approach close in - though sounds like it is YMMV on getting them to hold the new seats