Hi, yes, R1.
It might be easier to cut the trace that connects the resistor to VCC, which also makes the modification more easily reversible. Though now I look at it you don't need to bother. If you connect the L-pad via a coupling capacitor, then it makes no difference what's going on in the mic circuit with regards to DC. Try maybe 1uF to 10uF.
All that said, R1 is quite high and the module doesn't have an on-board regulator, so you are most likely perfectly ok doing your original plan anyway. Just account for R4 and R1 on the module being in parallel with R2 in the L-pad.
There might be a better way to do this however, if you are prepared for something a little more complicated, in the shape of an opto-isolator. The reason being the opto-isolator has an output transistor which you can connect directly in place of the mic and will probably provide adequate signal with no further modification. The other side of the opto is an LED which you can connect across the speaker, and depending on how powerful the signal is will need either a reverse diode across it and series resistor, or a small amplifier (1 transistor, coupling cap and a few resistors which would also need to connect the module's Vcc supply) Don't connect it direct it could blow the LED and distort the sound.
It all depends on how powerful your signal source is. Basically, the louder it is, the less effort you need to make!