It turns out that 09G was just 07G hardware with a minor change, so Davee created a tool to trick the PSP into accepting a lower firmware version than it shipped with.
http://lolhax.org/2011/09/01/chronoswitch-downgrader-5-0-advanced-09g-support/
(Since the 09G is mostly a 07G in disguise).
So you can try using his downgrade tool to put your PSP back to 6.20 is possible. If not you'll just have to deal with a temp hack, which just means it doesn't start up in hacked mode by default.
http://lolhax.org/2011/09/01/chronoswitch-downgrader-5-0-advanced-09g-support/
(Since the 09G is mostly a 07G in disguise).
So you can try using his downgrade tool to put your PSP back to 6.20 is possible. If not you'll just have to deal with a temp hack, which just means it doesn't start up in hacked mode by default.