I swapped mine from 8 to 9 - was a 10minute job. Swapping back should be as easy.
Drop the wheel, remove cassette, take big (10MM?) alan key to centre bolt, loosen, catch the pawls and springs carefully as the freehub body comes off (they can travel a looong way), slot 8 speed freehub in, checking pawls are correctly sprung and engaged, tighten up, reassemble. Job done.
If you need an 8 speed freehub, I have the one I removed safely in a box somewhere - if I can find it I'd happily swap.
Freehubs a ridiculously expensive - I ultimately bought a set of 9spd hubs cheaper than I could get a freehub on its own, then simply did the swap.
Not so much a six pack as a barrel!
1959 Carlton Continental 1982 Carlton Professional
1987 Peugeot Perthus Pro 753 1995 Colnago Superissimo
1995? Vernon Barker MTB 1993 Colnago MTB
2005 Colnago CT2 1978 Carlton Clubman