How to use the same switch to control LED and vary resistance?
You can simply use your 4 position switch to generate a control signal that then switches control elements (like MOSFETs).  You need to change your LED drives to this (note I only show one LED and One switch)







simulate this circuit &ndash; Schematic created using CircuitLab

Something similar can be done with the 555 as well,







simulate this circuit

Of course signal ctrl2, 3 etc. is not shown.

the main concern with this approach is two fold.

1)you must ensure that the gate swing is large enough that the transistor is remains fully conductive over the whole operational range.

2) if you put too large of a MOSFET in there the stray capacitance on the resistor chain will change the operating conditions.