if your reinstall is the same OS as before and you do not make any hardware changes it should reactivate

if this fails you can deactivate the previous config via the website

the 30 days rule is that you can only deactivate via the website once every 30 days - only a problem if you have already done this within the 30 days before your reinstall, in which case you can contact xara support and they should sort it oiut for you...