How does one go about changing a particular map's BGM?

Basically, this is what I want to happen:

Map A has S1 as its normal BGM. Sometime during the game, I'll use the Play BGM function on page 2 of Event Commands to change the BGM to S2. From that point on, when the character enters Map A, the BGM played will be S2 instead of S1. I don't want to use the Play BGM function every time I change maps because the BGM will have to restart everytime.

Any suggestions?

What I would do, is to don't have the BGM in the map properties, but in an autorun on the map.
That way, you can have different pages with different music, and change the page with a switch or variable.
But for the restart. I dont know. I'll try to make something when I come home.

That'll restart the BGM everytime, which is contrary to what I want to happen.

make 2 identical maps.

or. set s1 as the default. make an autorun event. with a control switch on. lets say control switch 004: BG change
then set your event that changes the music (maybe a battle that happens, or a jukebox) and add a command to initiate control switch 004. so, once that event is finished the bg music will always be s2.