Totally acceptable to do that.

Instead of cutting neutral wire, I would use it as a second ground. Tape it or use a marker to make it green, and it's even safer than before.

Only advice would be to splice it properly. Not sure if there's any 6 gauge marettes (wire nuts for Americans), but read the box and it will say if it's good for 6 and 8. If not, get one of those nut and u-bolt style ones, then wrap with the expensive 105° tape. Use an anti-oxidant such as noalux as well if its aluminum, just for code. If you want the noalux to work, make sure you rub it in with a wire brush, although this is unnecessary overkill in my opinion.

Edit: to clarify, this advice is all up to code in BC, Canada.