Im not sure about any change being made in its interior with the shape change as no one in our family is having or ever had a Santro so my information might be incorrect.
Santro was introduced in 1999~2000 just before Pak Suzuki launched Cultus in 2000.
That model of Santro was named as Santro Plus and its main noticable feature were its high mounted tail lamps.
The car was having a 12 valve engine with Multi Point Fuel Injection system.
Around 2002~2003 Santro was relaunched, and the marketing sentence that was used was "New style, Better comfort"
In this shape the front headlamps were changed with crystal headlamps and the taillights were brought down to a more normal position.
More over the rear bumper was also changed a bit and the reflectors in the rear bumper were no more in the new model.
The car at that time was having 2 trims i-e Club and Exec.
Later with the introduction of CNG by Hyundai in their vehicles we saw a GV variant aswell which was CNG fitted.
Another variant that was the base model was called as Santro Prime but that did not became that much popular.