I have sidelights on either side of my front door - the glass pane is
app. 7 ft in length. I'm about to replace the sidelight and I noticed
that the plastic (i think) frame that holds the glass in place has a
cut in it that divides the frame into two pieces. The cut does not
look like it was done in a factory or anything - it is a little rough,
so I am assuming that the installer cut the frame.

We get a lot of sunlight on that side of the house. Is the cut there
to allow for expansion of glass/frame? When I install the new frame
and glass, should I cut the new frame too? The house is 17 yrs old,
so is this no longer needed with the new materials that have been
developed since then?