Masking credit card numbers based on username

You would have to do it in a iRule.

To get the cookie you would do something like the following

set username [[HTTP::cookie] ]

Then you can compare the username to a data group to see if what policy to enable.

https://devcentral.f5.com/wiki/iRules.class.ashx

now the one thing I am not sure about is if you need to start the iRule with ASM::disable then enable it with the correct policy.