is there any way to multiplex/switch the current loop
How many?
if only a few, yuou will lose space by attempting to switch, if a lot the rules are:
1) the series resistor can not be switched
2) the analog switch must be placed at the 2 ends of the series resistors
3) the analog switch will blow if more than its Vmax comes down the 4-20.

So, you will need an analog switch powered by a fairly high +- voltage and still run a risk. I would NOT recommend that you attempt it, but can not state "you can't"

Erik