It's a little annoying for me to press F12 each time during PXE Boot as I do testing all the time.
Here are the steps to skip F12 :
On your WDS server(s) navigate to
Systemdrive:\RemoteInstall\SMSBoot\x64
Make a copy of your pxeboot.com (the version that prompts you to press F12)
Delete the original pxeboot.com
Make a copy of pxeboot.n12 (the version that bypasses the additional F12 prompt)
Rename this copy to pxeboot.com
Flag this file as READ-ONLY. If you do not do this the next reboot of your server will revert this file back.
Restart your WDS service and away you go.
https://wbracken.wordpress.com/2009/01/27/how-to-prevent-optional-pxe-adv-from-popping-on-clients/
PXE – How to Suppress F12 at PXE Boot
Here is an additional article about the detail boot files:
http://henkhoogendoorn.blogspot.nl/2012/02/pxe-boot-files-in-remoteinstall-folder.html