The Australian list of approved hymns is here. There is no permission for hymns from these books other than those listed. However GIRM gives no rule for the choice of post-communion hymn other thansuited to the sacred action, the day, or the time of year, and whose text has been approved by the Conference of Bishops.
as far as I understand the Latin it applies the praise requirement to any element including a hymn, but does not control the text.a Psalm or other canticle of praise or a hymn may also be sung
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