First and Most thank you for your interest in VONN. You may do it both ways, before installation or after. If it is done after the installation, please make sure that wires are not tide together inside the canopy because you simply won't be able to pull them down and lengthen the height. To shorten the height, please push the wires in to the desired length. Please do NOT cut wires, by cutting the wires, fixture will be damaged and warranty voided. Should you need any assistance do not hesitate to contact us again. Thank you!