Starting from the end. In Gerusalemme Liberata 4: 9, Satan lamented that they had been judged by God as "alme rubelle," rebel souls, i.e. spirits in this case - not "populace."
In GL, God was described as "Colui [che] regge a suo voler le stelle," He who rules the stars according to His will. The different wording in GC makes clearer reference to the very last verse in Dante's Divine Comedy: He who "move 'l sole e l'altre stelle."
But the most meaningful change concerns verse 5. In GL, Satan spoke of "gli antichi altrui sospetti," the early [literally: old, ancient] suspicions of 'somebody,' an indirect device to say God. While in GC Satan recalls "gli antichi miei pensieri," his own early thoughts. This also modifies the meaning of the second part of the verse, though the wording remains the same, i.e. "e i feri sdegni." That, with reference to God, might imply His "fierce wrath." With reference to the devil, it can be rendered as his "proud disdains." Both versions anyway can be read in a Miltonian key: the breaking of trust and confidence between Lucifer and God, and the former's plan to conquer heaven.
Last but not least, there possibly is a pun in verse 4. Satan points out "il gran caso" as the cause of their being in hell. In its older, Latinizing sense, "caso" means fall. But in Italian the term usually means "chance," therefore Satan - as he 'will again' do in Milton's Paradise Lost - may be suggesting that their defeat was due to mere chance, misfortune, bad luck.