[R] Changing a plot

[R Help]

Hello list,

I've been working on this problem for a while and I haven't been able
to come up with a solution.

I have a couple of functions that plot a bunch of data, then a single
point on top of it.  What I want is to be able to change the plot of
the point without replotting all the data.  Consider the following
example:

x = rnorm(100,1,0.5)
y = rnorm(100,1,0.5)
plot(x,y,pch=16)
points(x[35],y[35],pch=19,col=6,cex=3)

What I want to be able to do is to change the purple point to a
different value without replotting everything.

I know this seems like an odd suggestion, but it comes up a lot with
the work I'm doing.  I've prepared a package on CRAN called
ResearchMethods for a course I'm working on, and there are several
functions in there who's GUIs could work better if I could figure this
out.

If anyone has any ideas, or needs some further explanation, feel free
to contact me.

Thanks a lot,
Sam Stewart