If you mean an actual radio update for the phone, only stock recovery can flash them, AND you would need a stock(custom recoveries cannot flash them, since lg encrypts the radios) update zip of the baseband you are upgrading/downgrading to.
For prls yea you can just use qpst, if I remember correctly the latest sprint corporate prl is 25006.
Corporate prls offer better service and also allow you to 3g roam on other carriers. Be careful roaming however its not unlimited if you use more than 300kbs(its in the fine print on contract) sprint terminates you unless you have a roaming package on your account.
Just a side note you can go to settings and manually update the prl, since you are on a stock ROM it just won't work on a custom ROM.
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