9 Speed to 8 speed?
Can I simply remove the smallest cog from my 9 speed cassette to get my going on a 8 speed setup? J
Sort of, you will need to add a couple of spacers to get things to tighten up. Some pro XC racers do something similar, remove the 11 tooth then put the spacers behind the largest cog to move the hole cassette over. That gives them less chain deformation in the largest cogs and allows for better big-big performance.
This will not give you the main 8 speed benefit, more space between the cogs resulting in better tolerance for maladjustment and debris in the cogs.
The spacing of the 9 speed cassette's remaining cogs also won't match with an 8 speed index shifter. If you're just going to limit derailleur travel and still use your 9 speed index shifter it can work, but depending which cog you remove the shifting through the gap in the cassette won't be as smooth since the shift ramps will be misaligned.