Yes it is common to remove a section(s) of the boot to give it a softer flex.
I'll have to insert the requisite "Do not try this at home
" warning here...
Most boots, The Falcon Ten by Salomon for example, have a faint dotted line along the boot potion of the shell on which to remove material from the shell to make it softer. I usually am able to talk people out of this option because there may be another way to soften the boot. Sometimes there are rivets or bolts that connect the boot shell to the cuff to help stiffen the boot.
Remember: The is no "undoing" this procedure.