Oh that's disappointing, thanks for letting me know. I guess it will be a free for all on seats then as I do have a reservation but I understand these are invalid when a 170 is used in place of a HST. Luckily I am travelling through the week as I imagine this could be a nightmare during the weekend.
Only chance you have is if they cancel the 1714 from Inverness to Inverurie so the unit spare can do the run down to Edinburgh and then back up to Inverness and be their like the Inverurie one would be if it ran