What you can change while the printer is working
G-code is a list of instructions already calculated by the slicer: during a print you can only adjust values the printer or firmware allow to be overridden. Everything else needs a new slice.
Sources last checked: October 2026. What’s possible varies with model and firmware: always check your printer’s manual.
| Setting | During the print? | How | Caution |
|---|---|---|---|
| Speed | Yes | Bambu Lab: speed mode from the screen or app (official wiki). Klipper: M220 [K] | More speed needs more flow and Bambu printers don’t compensate: under-extrusion risk. TPU runs slower. |
| Nozzle and bed temperature | Yes | Bambu Lab: screen, app or Studio (official wiki). Klipper: M104 for the nozzle [K] | Stay inside the filament’s range: temperature also changes maximum flow and emissions. |
| Fans | Yes, with limits | Bambu Lab: screen, app or Studio (official wiki) | The profile’s cooling rules (for example on overhangs) take priority and can’t be changed mid-print (Bambu community note, unofficial). |
| Flow (flow %) | Depends | Klipper: M221 [K]. Bambu Lab: the community reports no live adjustment | To calibrate flow use the tests, not eyeballing. |
| Z offset (first layer) | Depends on the model | Klipper: SET_GCODE_OFFSET Z_ADJUST [K]. Bambu Lab: some guides describe adjusting from the display or app, the community reports it isn’t possible on some models | Small steps, 0.01–0.05 mm. Then carry the value into calibration, because a live change isn’t saved in the file. |
| Pressure advance and acceleration | Klipper only | Klipper: SET_PRESSURE_ADVANCE and M204 [K]. Bambu Lab: automatic calibration before printing | Change one value and note it. |
| Layer height, walls, infill, supports, seam, slicer retractions | No | A new slice and a new print are needed | The G-code already contains every move for those settings. |
[K] = Klipper documentation
Why some things can’t be changed
- The slicer turns the model into thousands of G-code lines: paths, plastic amounts and speeds are already written.
- The printer can only apply a multiplier (speed, flow) or an offset (Z position) on top of those lines.
- Changing layer height or infill mid-print would need a different path: that is why it isn’t possible.
Good practice
- Change one value at a time and wait a few layers to see the effect.
- Write down the value that works.
- After the print update the slicer profile: live changes aren’t saved.
- If the problem is serious (spaghetti, detaching from the plate), stop and restart: it often costs less than chasing it.