> considering surface friction is low enough for pieces to move
Our experience - which include track layouts that occupy a good proportion of the ground floor of our house, a la Wallace and Gromit's The Wrong Trousers Train Chase - is that if you open a section under tension, wiggle the entire track back and forth a bit, even on a solid wood floor it tends to settle into a "more relaxed" state, at which point you can adjust the relevant pieces to close the (often larger) gap...
Our experience - which include track layouts that occupy a good proportion of the ground floor of our house, a la Wallace and Gromit's The Wrong Trousers Train Chase - is that if you open a section under tension, wiggle the entire track back and forth a bit, even on a solid wood floor it tends to settle into a "more relaxed" state, at which point you can adjust the relevant pieces to close the (often larger) gap...