noob question about PSN SEN or whatever its called

I've been doing a lot of reading and can't quite pin down an answer.

What are the limitations around PSN/SEN with a modded/jailbroke ps3.

• Can I download and play the latest PSN games like Journey?
• Is there some way to toggle the current firmware on and off so I can quickly put my ps3 in a state where it can go online and then back to a state where I can play backup games.
• I read somewhere about cracking specific games so they can go online, is this the case?

If there is anything else you think I should know about the issue you please let me know.

Thanks!