An IF function is not included in the list of available functions for parameter management.
http://help.autodesk.com/view/ACD/2016/ENU/?guid=GUID-DBFA3E85-2055-4698-85FD-6B30D39F3FA4
You could use a combination of the -parameters command and Autolisp to make a conditional relationship between dimensions. I have limited lisp experience but may take a stab at it if you are interested. For example, the command could take the the form of:
ChangeDim dimIn dimOut condition true false
dimin = parametric dimension you want to change
dimout = parametric dimension changed by a conditional expression
condition = the expression to evaluate
true = action if condition is true
false - action of condition is false
lee.minardi
