There is no way to 'login' in PSN if you have lower firmware than required one in PSN. The only thing you could do - get your profile id from psn and 'activate' your local account this with profile id and then if you have your save files local - they gonna work without extra steps probably.
I...
How you managed to do this? Tried to use old ps store with valkyrie extension and it just doesn't work. Trying to get a link to purchased pkg from my account.