Not looked for ages so don't know, you are best off doing a google round there are possibly new ways to mod the console now anyway just google Vita softmod and see what comes up
Officially no you can't downgrade, if there is a homebrew way to downgrade you would need to do that via a softmod anyway
Sony has an online store it is called PSN (PlayStation Network), those that subscribe to Playstation Plus aka PS+ get free software every month
I can't see any hacked consoles being able to connect to PSN though anyway, just blacklisted.
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