LTSPICE allows control of the resistance of a standard resistor element by a voltage source. This can be used to set up the time variable resistance of a resistor by creating an equivalent time variable voltage source.
To do this, set up a voltage source and label the voltage source's output net with a descriptive name (e.g. Vresistance). In the value field of the time variable resistor set the value to R=V(Vresistance). Set up the voltage to represent the time variable behavior as expected, using e.g. PWL statements or any other suitable waveform.
1 V is equivalent to 1 Ω, 1 kV is equivalent to 1 kΩ etc.
Example: a resistor with a resistor varying sinusoidally between 10 Ohm and 30 Ohm at a frequency of 100 Hz.
Figure 1-1 Example circuit showing time variable resistor.
Based on this source: http://electronics.stackexchange.com/questions/3623/ltspice-vary-a-resistors-value-over-time
SPICE help topics to look at: R., Resistor
Harald Kapp, 2017-02-08