Hi Hobbit,
If you disable STP on the non-root bridge first and then disable STP on the root bridge, the services will not be affected.
If you disable STP on the root bridge first, the interface status on the switch will unchange and be still in the forwarding state. But if the none-root bridge does not receive BPDUs from the root bridge within the timeout period, it will set all the interfaces to the block state, and calculate the spanning tree. After the calculation is complete, all interfaces on the device will be set to the forwarding state. In this case, services will be interrupted for a short period of time.