So, my printer's default ABL mesh was 5x5 points, but there are issues with my bed, between those points. I got a custom firmware that changed it to 15x15, but I have a few spots that still rub my prints. Can I just do a one-time 25x25 mesh build using G29 J25 through OctoPrint? If so, would I add that command before the G29 P1? Thanks for any info.
G29 J<value> for UBL meshes probes with that number of points to generate a plane, not a mesh, and then 'tilts' the existing mesh to fit this plane. It won't create a mesh of 25x25 points, which is what it sounds like you want. As far as I know you can't change the mesh size without recompiling Marlin (assuming that's what you're using).
Info from Bed Leveling (Unified) | Marlin Firmware (marlinfw.org)
Thanks. I was basically seeing if there was an option to shortcut recompiling (my next journey) and use gcode options.