Internet Expense - Expense Categories

Hi,
I have come across a situation while implementing Internet Expenses

Scenario:
Currently the users, submit expense claims for "Cleaning Materials", "Staff Refreshments" etc. And as far as the expense categories are concerned we have the below mentioned seeded categories

a) Car Rental
b) Accommodations
c) Miscellaneous
d) Per Diem
e) Air Fare
f) Meals
g) Mileage

And I have also come across a note which says the lookup which maintains these categories is defined with a system level access and it is not advisable to update this lookup. Hence to handle our scenario, we are planning to define "Cleaning Materials", "Staff Refreshments" etc as Expense Item and the category as miscellaneous. Do we have any other better way to handle this scenario?