TL;DR: Identity and OASIS credentials, while both using retina scans, are different things and not connected. And Wade doesn't use OASIS while at IOI.
When Wade first moves to Columbus, he creates a new identity and moves (not copies) his retinal information to the new identity (emphasis mine):
I was able to purchase a series of access procedures and passwords
for the USCR (United States Citizen Registry) database. Using these,
I was able to log into the database and access my existing citizen
profile, which had been created when I enrolled for school. I
deleted my fingerprints and retinal patterns, then replaced them with
those of someone deceased (my father). Then I copied my own
fingerprints and retinal patterns into a completely new identify
profile I'd created, under the name Bryce Lynch.
However, after he does this, he remains able to access his OASIS account via retinal scan. So clearly the OASIS database isn't reliant upon the USCR for identity management.
Now, the next obvious problem is, if OASIS continues to authenticate using his true retinal data, wouldn't it be awkward when Parzival popped up when he logged in at IOI headquarters as an indent? However, when he's working as an indent for IOI, he's not actually logging into OASIS, he's logging into an IOI internal account:
My employee ID was verified and I was automatically logged into my
work account on the IOI intranet. I wasn't allowed to have any
outbound access to the OASIS.
IOI's intranet was a high-security, standalone network with no direct
connections to the OASIS.
It's clear that there's layers of software mediating Wade's interactions with actual OASIS users while he's working support calls for IOI:
IOI's patented customer courtesy software had detected the
inappropriate nature of my response and muted it, so the customer
didn't hear what I'd said. The software also logged my "courtesy
violation" and forwarded it to Trevor, my section supervisor, so that
he could bring it up during my next biweekly performance review.
So, to sum up:
- Wade could change his identity without altering his OASIS access because they're different databases.
- Wade's unchanged OASIS identity didn't hinder his stint undercover at IOI because they didn't grant him actual OASIS access.