The World Superbike rider was drafted in by Honda as a replacement for Casey Stoner following the 2011 world champion's ankle injury at Indianapolis and subsequent decision to return home for an operation.
Stoner's injury also coincided with Brno and Aragon tests, allowing Rea three days of testing in the build up to the San Marino Grand Prix.
Having moved to within 1.8s of Pedrosa on the final day of testing he says he is ready for the challenge, even if he is still building up his experience and pace.
"For me its a big dream come true just to race in MotoGP," Rea said.
"It's been very unfortunate for Casey to sustain such an injury when he was having a very strong season and my best wishes go to him while he recovers.
"Now, my job is to replace him and I will try to do the best I can.
"I take this opportunity like a great gift from Honda; in the few days I've spent with the team I have felt very good, they understand it will take me some time to push with this bike but I'm learning every time I get on it.
"It's been great to have these three days testing on the bike to prepare myself and for sure Friday morning will be less chaotic. We already have the riding position set, the base setup is set and I understand the electronics a little more.
"I know it's going to be busy, but I'm ready."
Rea has a strong World Superbike record at Misano, finishing fifth and second in this year's races and also claiming his breakthrough win at the Italian venue in 2009.
He is expected to also stand in for Stoner at the following Aragon GP, with the Australian targeting a return at his home race at Philip Island.