Since RailClone 3 we have more powerful expression editor, though it requires a little modifications from v2.
expression "-1*(Input/4)" in v2 should be written in v3 like this:
in Your example "=" should be replaced with "=="
You should add "return" in start of "expression" and end it with ";"
so Your example in RC3 should be written like this:
return if (YSplinePosition==0,3,if(YSplinePosition==1,1,2) ;
Hope this helps.