No way from standard Gimp options. Two possibilities.
1) Use a script to set the guides: The simplest is here: Greggs crosshairs https://www.gimp-forum.net/attachment.php?aid=4171 There are others.
That registers in the layers menu. To avoid the menu assign a keyboard shortcut key.
2) If the canvas size is constant. Make a blank canvas. Set the center line guides. Save the canvas as a Gimp .xcf . All guides / layers / channels / active selections ... are saved. Instead of Image -> New Open the .xcf you made.
1) Use a script to set the guides: The simplest is here: Greggs crosshairs https://www.gimp-forum.net/attachment.php?aid=4171 There are others.
That registers in the layers menu. To avoid the menu assign a keyboard shortcut key.
2) If the canvas size is constant. Make a blank canvas. Set the center line guides. Save the canvas as a Gimp .xcf . All guides / layers / channels / active selections ... are saved. Instead of Image -> New Open the .xcf you made.