Modifying a mask requires four things. :
A Mask
A material
A Pattern
A colour scheme
When out have obtained all four items from cards (at the end of a successful job), you need to head to your inventory, select the mask and press
to customise.
You can then select which variables of pattern/material and colour you want to use.
When your happy with your selections confirm them, and the achievement will unlock.
This usually costs in the region of 200k spendable cash go complete.