We recently had to replace our main due to squirrel damage.
Found a replacement at a sail loft, but now the boom hangs considerably lower, almost to the traveler.
I assume we ended up with one that’s not a one design main by measure…
1. can I reef it and still get good performance?
2. will this be a benefit in light wind?
No. 2: conceivably, but it doesn't sound like what you should use. Almost to the traveler isn't good. I assume then that the boom would hit the lifelines on a reach.
No. 1: I don't know. I haven't used a J/24 main with reef points (the major sailmakers haven't put reef points in since the 70's). We'd have to see how it looks.
I think you should talk to the sail loft. Maybe they can re-cut it. Maybe they'll take it back. Presumably they sold it to you with the understanding that it would work on a J/24. I assume that it's not really a J/24 main though.