First of all, you shouldn't set gc_grace_seconds to 0, unless on a single-node cluster. If gc_grace_seconds is set to some period, you must run repair at least once in every such period, otherwise you have a risk of data resurrection - which happens when one node on the cluster missed a deletion, and other nodes drop their tombstones, so a later repair will think the data is new and not realize it had been deleted already. If you ever set gc_grace_seconds to 0, any data which you previously deleted may be resurrected on the next repair, if the data happens to be on one of the replicas (because this specific replica missed the deletion because of some temporary problem).
So yes, the correct approach would be to run a major compaction with the original gc_grace_seconds of 10 days (and be sure to do a repair at least once every 10 days).
But you need to consider why you want to run a major compaction at all. Whether or not minor compaction can get rid of old (past 10 day) tombstones depends on a lot of factors, such as whether you recently made other modifications to the same partition that these tombstones sit in. But unless the tombstones are causing you major problems (tons of disk space, slower reads, etc.), it might not be worthwhile to do a major compaction. Major compaction is not free, and (at least in size-tiered compaction strategy) after it, all the data is sitting in one file and will take even longer until it can be compacted again.
