Hi onesixright,
In the schematic library editor, select all objects in the part by pressing Ctrl+A, then press F11 to open the Inspector. Filter to only show Pins by setting the Inspector to Include only Pins.
Change the length and click out of the Length field and then the pins in that part will change length. Please see attached screen capture, changing pin length for part C of the FPGA.
To change another Part in the component, click the part such as Part B, then click on the editor background twice to deselect so that the inspector is empty, then press Ctrl+A again to select the objects in that part and change those pins in the Inspector panel.
P.S.
The example SpiritLevel project I'm using in my screen capture can be downloaded here:
https://www.dropbox.com/s/93ryocdcu8w5b3n/SpiritLevel-SL1_CS.zip?dl=0Best regards,
James Harriman
Altium