Doxology = reverence to the name and the presence of Our Lord. Accordingly, every time there is a doxology, such reverence is merely logical. What's even more at the mention of the Holy Name of Jesus, (such as in "Sit nomen Domini benedictum in saecula") a similar reverence should be shown.
Yes. I have seen variations at doxologies that are not “Father, Son, and Holy Spirit” (like the Incarnation doxology that only names the Father and the Spirit and names either “Domine” or “Jesu” depending on the text) where you bow for only part of it. Ditto the psalms: in ps 110, ps 112, and sometimes 113 (for the entire verse Non nobis), following the LXX/Vulgate numbering.
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