How can I limit the voltage value of a net within a certain range in LTspice. For example, I want to supply a voltage to my model which will act as the duty cycle control so its value must be between 0 and 0.9, but the output of the Gcv block is higher and so I need to restrict it in the range above.
If LTspice supports full Spice then there are MAX & MIN parameters you can add to a G source. However, I suspect it doesn't. If so you will gave to try to construct some more complex circuit to get round it.
A couple of switches which are triggered when the output of the G source reaches a certain value and changes the output to a fixed voltage may do the trick.
Consult the LTspice manual for the description of the "B" Arbitrary behavioral voltage or current source element.
It allows powerful behavioral circuit definition, e.g. using a max() function in your case.