You cannot access idn rule utilities in aftermodify rule. The rule is nothing but powershell script.
You have 2 options:
Use before provisioning rule and add all extra account/identity attribute you need under plan arguments and then read those in your aftermodify rule.
Call identitynow apis back and get those attributes.
If your account/identity attribute somehow are dependent on Ad then you can also explore option of calling AD powershell functions and get those values.
In my knowledge only those which I listed above. The rule executes on Iqservice machine and all objects which are stored on cloud database can be only accessible by the rules which are executed on cloud , like before provisioning rule for example.