Hello:
I have not used yet IT0793 as I found 0874 easier to manipulate; however if you follow the link I gave you there is a pretty neat example. Looks at this scenario, it state how NIC is affected:
NIPE Process Scenario - Payroll Great Britain (PY-GB) - SAP Library
Used IT0874 a couple of times; it adjust or not Tax paid wage type (/501) Employee NIC wage type (/301) Employer NIC wage type (/302) depending if you have set an amount in the corresponding Inoftype screen field.
Year to end, nor other processes are affected since it adjust directly the final secondary wagetype representing either NIC or Tax that legal reporting is reading to output.
Best.