How to safely change PWM frequency(or arr) after `finalize()`?

[Joker2770]

It seems that there is no relevant function about changing PWM frequency after the finalize() be called.
I use the unsafe way at present. I don't know if it is logical as follow.

    let pwm_t4_c3_builder = dp.TIM4.pwm_advanced(...);
    let (_, mut pwm_t4_c3_ctrl) = pwm_t4_c3_builder
        .prescaler(...)
        .period(...)
        .finalize();
    pwm_t4_c3_ctrl.set_duty(...);
    pwm_t4_c3_ctrl.enable();

    // change arr
    let tim_4 = unsafe { &*<pac::TIM4>::ptr() };
    let _ = tim_4.arr.write(|w| w.arr().bits(...));

Somehow the duty and cycle need to be change continuously at runtime. Is there a safe and efficient way？