Preseeding in Ubuntu installer

I want to run a few commands immediately after installation of Ubuntu.Therefore I thought of using preseeding concept.I extracted my iso and in the preseed folder appended the following line to custom.seed file

d-i preseed/late_command string in-target mkdir /home/abc

Now I repacked the iso and installed ubuntu using it..But no change happened..What am I doing wrong here?

I recently had a lot of frustration preseeding xubuntu 20.04 desktop. Ultimately this is what worked for me:

From "using preseed files" in UbiquityAutomation.

Specifying a preseed file is not enough, the boot code 'automatic-ubiquity' or the ubiquity command with the --automatic argument is also necessary.

The iso txt.cfg/grub.cfg starts up with only-ubiquity. So, if you did not modify those files and just added the preseed file and then repacked, it will not work.