mr-marty-martin said:
will go on but you will have to add more spacers on the inside, or outside of the cassette
No you won't - you will have to
remove a spacer, as palinurus says.
A few years ago, Shimano made a small number of wheels which were 10sp only : a few Ultegra & Dura Ace wheels with an aluminium freehub - 105, Tiagra, current Ultegra & DA, anything Shimano with a steel or titanium freehub are fine.
There are also some aftermarket Shimano-10sp-only wheels, but they're fairly unusual, the vast majority of Shimano-fit wheels are 8/9/10sp-compatible.
A 10sp cassette is
narrower than 9sp or 8sp, so it's 10sp which needs the spacer.
When you remove your 10sp cassette, you should find a thin spacer (aka big washer about 1.something mm thick) behind it.
Take that off and put your 8sp cassette on without it.
If you're lucky, depending quite how the axle is spaced, you may find your rear mech is correctly adjusted and you can just swap-in the wheel without any adjustment.
If not lucky, should just be a few turns of the adjuster and maybe the top or bottom limit screws.