What George said, along with NOT getting your sheet lines crossed too, assuming you are like me, with sheets for all 4 of the HSails I have.
Then at least here in PHRF-NW, you can peel if in a FS fleet, if racing NFS, you can not peel, you need to let the old sail ALL the way down before you raise the new HS. You can put the new HS in the groove, no higher than 5' IIRC ready to hoist when the old sail is on deck.
She drives me boat,
I drives me dinghy!