Use msiexec /p [path to image]. But you'll still need to
trigger upgrades at each user, using msiexec /i
It's probably worth a look at this thread also, particularly at the
batch files that Jason Capriotti uses for his users to update from
the image:
https://forum.solidworks.com/forum/messageview.cfm?catid=22&threadid=9551&enterthread=y
Just go to the Solidworks website and manually download the
SP. double-click the SP download and it will ask you if you want to
patch an individual installation or an admin image. Pick admin
image and point to your image .msi.
It's probably worth a look at this thread also, particularly at the batch files that Jason Capriotti uses for his users to update from the image: https://forum.solidworks.com/forum/messageview.cfm?catid=22&threadid=9551&enterthread=y