Mr Evans said the changes were likely to see some testing stations close and others reduce services.
"It's early days yet, but quite obviously the demand for WOFs will decline, and that will have an impact on our business," he said.
Under the new regime announced on the weekend, six-monthly warrants will be phased out for cars registered after January 1, 2000, with only annual checks required. Older cars will still require six-monthly warrants.
And the WOF demand eases for new vehicles too. After an initial warrant, no further testing would be required for another three years.
The Government is planning to have the changes in place by July 2014, or even earlier.
Mr Evans said his organisation would have to "work very hard" to handle the impact of the changes.
"From every downside, we believe an opportunity can be developed. Our business is built on a strong and loyal staff, and they will be our major priority," he said.
He said while the Wanganui service worked out of two buildings there may be consideration given to having them under one roof, as happens in some other centres, "but, again, that's still to be looked at".
He said VTNZ also had concerns with changes flagged for COFs. Currently, heavy vehicles and light vehicles operated as a transport service, such as taxis and rental cars, are inspected for a COF usually every six months.
There are only three organisations approved to provide COF inspections (including VTNZ) but none of these provide repair services. However, Mr Evans said under the changes owners and operators will have a much wider choice about where they get their vehicles inspected, with those places able to combine inspection and repairs.
"Our major concern is that this sort of competitive pressure could lead to a lowering of standards and this country does not have a great record in terms of self-regulation," he said.
He said removing the existing safeguards meant a bigger investment in auditing, compliance and enforcement, but without those safeguards it could prove very hard to protect the integrity of the inspectors.