Not a pacemaker, but a similar situation. My oldest son just had a VNS installed (Vegus Nerve Stimulator). Very close to a pacemaker by design, it just functions differently. It is used to break up epileptic neuro-pathways by imparting a voltage directly to the vegus nerve. Anyhow, it comes with a magnet that you can swipe to turn it up during a seizure, but reading the full pamphlet showed other uses for the magnet.
It comes with the exact same warnings. No welding, no MRI, no high-frequency waves, avoid commercial antenna installations.... Turns out that it is completely MRI safe, the warning is there because some lawyer thought it should be. (They did an MRI to confirm its placement after the surgery!)
Since this device is used near the vocal chords, it can interfere with speaking. You can tape the magnet right over the device (on your skin) to disable it for periods of time to give a speech or to sing. I would imaging that they could do the same thing with a pacing device.
The best thing you can do is be completely honest with your doctor and let him know how important it is...AND...take his advice, he probably knows what he is talking about too!