Cherries are definitely more tolerant to high GH than nitrate, as long as it's not changing too quickly. So play with the amount of crushed coral is ok.
WC can get the nitrate down for sure, but you need to find out why your nitrate is high and fix the source. I've done 20% everyday for 4 or 5 times within a week trying to get nitrate down for my CRS/OEBT tank and there was no issue. I'm sure cherry can take it.