Every 3D printer or machine tool that is commanded through G-code must interpret the G-code in terms of the particular mechanism. Even a Cartesian machine in which there is a clear X, Y, and Z axis, each with independent actuators, interprets the G-code and adjusts for the scale factors, considers the current kinetic energy and the implicit changes in the kinetic energy, and constructs a move plan to implement the G-code. This involves considering the velocity limits, the acceleration, the jerk, and possible higher derivatives. This plan is passed to the motor drivers, and the mechanism responds.
A delta mechanism is really the same. The difference is that there is not a distinct X, Y, and Z axis, even though the commands in the G-code are given in Cartesian coordinates.
My second 3D printer is one I designed using standard hot ends and extruders. I'm using the reprap firmware, and haven't adequately studied the kinematics.
My first milling machine, however, was a delta machine with 3 additional degrees of freedom -- a machine style generically called a parallel-kinematics inverted Stewart platform. In my kinematics code, I plan a movement by breaking the Cartesian command into small enough segments that the non-linearity of the 6-axis movement space never exceeds the tiny error of the actuators. I developed a CPU-intensive but effective calibration system that estimates the errors that I introduced when building it, and so the mechanical performance is good enough. The machine itself is a 5'x6'x6' frame of welded steel, so it is pretty dimensionally stable.
A delta 3D printer is simpler because there is no control over the roll, pitch, and yaw of the hot end. Unfortunately, not being able to control also means that you are subject to whatever errors are introduced in the construction.
"Bed-leveling" of a delta printer consists of estimating some of the machine-unique parameters and compensating for their effects: cup, bowl, ripple, and tilt. Applying these adjustments is done in the kinematics code as a further modification of the G-code Cartesian parameters to the leg-space delta mechanism motions.
The G-code is not modified, but the parameters expressed in the G-code are adjusted and interpreted in light of the machine kinematics so that the intention of the G-code can be faithfully followed.