For Schnoor signature aggregation, could you save the midstate for a tagged hash? Since it's hash(hash(tag)||hash(tag)||message)
You could save the midstate and just start with the message from that midstate.

Does this make sense?

nostr:nprofile1qqsfrkatna3xvr54ykzgp5hjelmdeld4z0eg4p06f764a6vn5k6xszgpr4mhxue69uhkummnw3ez6ur4vgh8wetvd3hhyer9wghxuet5qyw8wumn8ghj7mn0wd68ytnzd96xxmmfdejhytnnda3kjctvqydhwumn8ghj7mn0wd68yttsw43zuum9d45hxmmv9ejx2askw6tvd nostr:nprofile1qqsdnpcgf3yrjz3fpawj5drq8tny74gn0kd54l7wmrqw4cpsav3z5fgpz4mhxue69uhk2er9dchxummnw3ezumrpdejqz9rhwden5te0wfjkccte9ejxzmt4wvhxjmcprpmhxue69uhhyetvv9ujuumwdae8gtnnda3kjctvl3x2lg 

 You mean the midstate of hash(hash(tag)||hash(tag))? If so, yep! Thats what happens :-) 

 Yes!