I think that McKenzie Method is quite safe both for acute and chronic conditions of the neck disorders. Infact it may improve early recovery in both Neck and Lumbar problems. So you may safely continue with that as McKenzie approach consists of comprehensive assessment and treatment consisting of Cause and effect.

Apart from that you may continue with Cervicothroacic stabilization programme (Flexibility, Postural Training, strengthening) a very good way of improving the neck disorders.

Spinal mobilization and manipulative maneuvers are effective in relieving the pain but does not alter the course of condition in long term; so don't worry about that.

Please see if neural tension test are postive for cervical spine and lumbar spine, you may start with nerve mobilization maneuvers.

Assess the progress of patient by reassessing and pain charts.