modify schematic net expressions with skill

[danmc]

Hello,

I have a bunch of schematics that all have a couple of labels on wires
which are net expressions. I want to change what the default net is
(VDD! -> vdd!). I can't seem to figure out how to do this with skill.
I tried

cv = dbOpenCellViewByType( "myLib" "myCell" "schematic" "" "a")
foreach( sig dbGetCellViewInheritedSig(cv)
ne = dbGetSigNetExpr( sig )
dat = dbParseSigNetExpr( ne )
scope = nth(0, dat)
prop = nth(1, dat)
str = nth(2, dat)
defnet = nth(3, dat)

cond(
( (prop == "VSS") defnet = "vss!")
( (prop == "VDD") defnet = "vdd!")
)

new = sprintf(nil, "[%s%s:%s:%s]", scope, prop, str, defnet)


dbReplaceSigNetExpr( sig new) )
)

schCheck( cv )
dbSave( cv )

but that isn't quite right. The dbReplaceSigNetExpr() call returns
"t", but I don't see any change to my schematic.

Thanks
-Dan