Change the FetType using skill

Hi, 

I wanted to change the Fet type of a mos instance from egnfet to lvtnfet (or any other type).

Currently I am using this snippet for a cell view with only one instance.

cv=gegetWindowCellView()
x=cv~>instances
schReplaceProperty(list(x)  "fetType"  "lvtnfet")

after executing this snippet 

when I type 
x~>fetType 

it displays "lvtnfet".

But when I generate the CDL, the fetType is still displayed as "egnfet".

I am able to change every other cdf parameter using the above snippet and it is also displayed in CDL correctly except fetType.

Please tell a solution for the problem.

Regards
Utkarsh