Risk of long-term shorting XLR cable
This may be most easily understood by looking at an old-fashioned transformer balanced configuration.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. A phantom-powered microphone circuit using balanced / unbalanced transformers and a mute switch.

How it works:


The 48 V supply is fed in the centre-tap of XFMR2. Current splits both ways in the transformer with the result that the DC current is running opposite directions in each half of the winding so the flux in the core cancels out and the transformer doesn't saturate.
At the microphone end the reverse happens and the 48 V is collected, smoothed and used to power the microphone preamp.
Return current is through the screen or shield wire (pin 1 on an XLR).


Now have a look at your MUTE switch. It shorts out the audio but for the DC it is only connecting one 48 V line to the other. It does not load the power supply or short-circuit it in any way.

Also note that the preamp remains powered so unlike your other question where you proposed to cut the phantom power lines this circuit should not give an audible "pop" when un-muted.