You are changing the battery yes, but when you do that, do not connect the discharge wire to the bms. Just connect it to the XT connector instead. Then use the bms charging wires and solder them to the battery positive side for charge only.
That’s all you need to do. Do note that some bms will need to be soldered in the voltage order for charging to work. I had this issue and had to re-solder the wire to where it goes for it to charge.
Like so. This was before I properly covered and neat cleaned my wires. If you see a black and blue wire, that will go to the negative side of the battery, the same for the discharge wire.