If you haven't CUT OPEN sealed security labels such as HDD come in, or sliced off WARRANTY VOID IF REMOVED labels, or done something IRREVERSIBLE like applying CPU paste
then opening the product, even powering it up (provided this is reversible - as it would be for a fan) should
IMO be fine to return PROVIDED all the packaging, manuals, cables, connector pins etc are all unaffected, and the item can be resold
AS NEW.
Note resold AS NEW.
IIRC under DSR you are not required to pay a restocking fee. Guidance available from the OFT here:
http://www.oft.gov.uk/shared_oft/bus...ral/oft698.pdf