If my work arrangement changes over time, can my corporation later be reclassified as a personal services business?

Yes. Personal services business status isn't a one-time determination fixed at the moment you incorporated, it depends on the ongoing substance of your working relationship, so if the way you actually work changes over time, your corporation's classification can shift too, in either direction. Taking on additional genuine clients, gaining more control over how and when you work, or starting to bear real financial risk can move an arrangement away from PSB status; conversely, a corporation that started out serving several independent clients could drift toward PSB status if it ends up working almost exclusively and closely under one client's direction.

Because CRA looks at the relationship as it actually existed during each specific period or tax year, a reassessment covering multiple years can, in principle, find that a corporation was a genuine active business in earlier years and a PSB in later ones, or vice versa, depending on how the facts actually changed.

This means PSB risk isn't something to assess once and forget, anyone whose working arrangement has shifted meaningfully, in client count, control, or financial risk, should periodically reconsider where their corporation currently sits against these factors rather than relying on an assessment made years earlier.