A meter change mid-piece is currently inexpressible, and its placement convention must be specified for when it becomes possible

When the meter changes, the new time signature prints immediately before the barline that begins the new meter's first bar. When a system break falls at or near the meter change, convention ALSO prints a small courtesy time signature at the very end of the previous system, so a performer reading ahead sees the change coming across a page/line turn.

Gould, Behind Bars, ch. 'Time signatures', meter-change placement and courtesy-signature convention; Ross, The Art of Music Engraving, agrees on courtesy-signature placement at system ends.

This rule needs the notated content and the rendered result together — the score says what should happen, the page says whether it did.