Is it possible to add conditional logic to a PXELINUX configuration file?

We have a system where an SBC will use TFTP to pull down a boot-loader configuration.

1. If the SBC is a UEFI system, it will pull down a GRUB2 configuration.
2. If the SBC is a BIOS system, it will pull down a PXELINUX configuration.

Then the SBC will use the boot-loader configuration to PXE boot into an operating system whose image is served over NFS. With either type of boot-loader, the configuration must read a file on the hard disk to determine some kernel command line parameter.

This is straightforward on the GRUB2 configuration. Here is what example code looks like for this configuration:

set timeout=0
set default=0

if [ -e (hd0,1)/some_predetermined_file ]; then
    echo 'Found indicator file.'
    set default=1
fi

menuentry 'CentOS 7 Option 0' {
    linuxefi /images/vmlinuz $cmdline
    initrdefi /images/initrd.img
}

menuentry 'CentOS 7 Option 1' {
    linuxefi /images/vmlinuz $cmdline other_parameter
    initrdefi /images/initrd.img
}

My question is, is it possible to have conditional logic like this in a PXELINUX configuration? Proposed is something like:

default centos-0
display help.txt

[ -e (hd0,1)/some_predetermined_file ] && default centos-1

label centos-0
  kernel vmlinuz
  append initrd=initrd.img $cmdline

label centos-1
  kernel vmlinuz
  append initrd=initrd.img $cmdline other_parameter

I have read through the configuration file specification at https://wiki.syslinux.org/wiki/index.php?title=PXELINUX but nothing jumps out at me as the right way forward. Maybe general scripting and/or disk access in the PXELINUX environment is impossible, or it is so obvious it goes without saying. Many thanks.